Step 1: Prepare Your Ingredients and Baking Equipment. Before mixing the cookie dough, measure all ingredients carefully and allow the unsalted butter to soften to a cool room temperature, ideally around 65–68°F (18–20°C). The butter should yield slightly when pressed with your finger but should not look shiny, greasy, or partially melted. Bring the whole egg and additional egg yolk to room temperature so they blend smoothly into the mixture. Line two baking sheets with parchment paper and prepare a large mixing bowl, medium mixing bowl, electric mixer, and cookie scoop. Do not preheat the oven yet, because the dough will need to chill before baking.

Step 2: Combine the Dry Ingredients. In a medium mixing bowl, add 2¾ cups (344 g) of all-purpose flour, 1 teaspoon of baking powder, ½ teaspoon of baking soda, and ½ teaspoon of fine salt. Whisk thoroughly for approximately 30 seconds to distribute the leavening agents and salt evenly throughout the flour. This step helps the cookies bake consistently and prevents concentrated pockets of baking powder or baking soda. For the most accurate results, weigh the flour using a digital scale. If measuring with cups, spoon the flour into the measuring cup and level the surface without packing it down, since excess flour can make the cookies dry, heavy, or crumbly.

Step 3: Cream the Unsalted Butter and Sugar. Place 1 cup (226 g) of softened unsalted butter and 1½ cups (300 g) of granulated sugar into a large mixing bowl. Using an electric hand mixer or stand mixer fitted with the paddle attachment, beat the ingredients on medium speed for approximately 2–3 minutes until the mixture looks lighter in color, creamy, and slightly fluffy. Stop once or twice to scrape the sides and bottom of the bowl with a rubber spatula, ensuring that the butter and sugar are evenly incorporated. Proper creaming helps establish a tender cookie texture, but avoid excessive whipping, which can introduce too much air and encourage unwanted puffing or uneven spreading during baking.

Step 4: Add the Egg, Egg Yolk, and Vanilla Extract. Add 1 large room-temperature egg, 1 additional egg yolk, and 2 teaspoons of pure vanilla extract to the creamed butter and sugar mixture. Beat on low to medium speed for approximately 30–60 seconds, just until the ingredients are smoothly combined. Scrape down the sides and bottom of the bowl to incorporate any remaining butter mixture. The additional egg yolk contributes richness and tenderness, while the vanilla extract enhances the naturally sweet, buttery flavor of the cookies. If the mixture initially appears slightly separated, continue mixing briefly until it becomes reasonably uniform, but avoid overbeating once the eggs have been incorporated.

Step 5: Incorporate the Dry Ingredients and Form the Dough. Add the prepared flour mixture to the wet ingredients in two additions, mixing on low speed after each addition until the flour is almost incorporated. Stop the mixer as soon as only a few small streaks of flour remain, then use a rubber spatula to gently fold the dough together until no dry flour is visible. The finished dough should be soft, thick, and slightly tacky without being runny or excessively sticky. Avoid prolonged mixing because excessive gluten development can make the cookies tougher instead of tender. If the butter was properly softened and the ingredients were measured accurately, the dough should hold together easily without needing extra flour.

Step 6: Portion and Shape the Sugar Cookies. Using a 1½-tablespoon cookie scoop or a kitchen scale, divide the dough into approximately 24 portions of about 38–40 g each. Roll every portion gently between your palms to create a smooth, round ball without compacting the dough excessively. For an optional lightly crisp, sparkling exterior, place ¼ cup (50 g) of granulated sugar in a shallow bowl and roll each dough ball in the sugar until evenly coated. Arrange the cookie dough balls on a parchment-lined baking sheet or tray, leaving some space between them. Keep the dough balls rounded rather than flattening them heavily, as their shape helps produce thicker cookies with soft centers.

Step 7: Chill the Cookie Dough for Better Texture. Cover the portioned cookie dough loosely with plastic wrap or place it in a covered container, then refrigerate for at least 30 minutes. Chilling allows the butter to firm up and the flour to absorb moisture, helping the cookies maintain a thicker shape and reducing excessive spreading during baking. If your kitchen is particularly warm or the dough feels very soft, extend the chilling time to approximately 45–60 minutes. For longer preparation, the dough balls may be refrigerated overnight in an airtight container. If they become very firm, allow them to stand briefly at room temperature while preparing the oven, but keep them cool when they go into the oven.

Step 8: Preheat the Oven and Arrange the Cookies. Near the end of the chilling period, preheat your oven to 350°F (175°C), using the conventional bake setting, and position an oven rack in the middle. Line a light-colored baking sheet with fresh parchment paper if necessary. Arrange the chilled dough balls approximately 2 inches (5 cm) apart, leaving enough space for moderate spreading. For even baking, place only one baking sheet on the center rack at a time whenever practical. Avoid placing cookie dough on a hot baking sheet because the butter may begin melting before the cookies enter the oven, increasing spreading and affecting the final texture.

Step 9: Bake Until the Edges Are Lightly Golden. Place the baking sheet in the preheated oven and bake the sugar cookies for approximately 10–12 minutes, checking them closely beginning at 9 minutes. The cookies are ready when their edges look set and very lightly golden while the centers appear slightly soft and just set on the surface. They may look a little underdone in the middle, but they will continue firming as they cool on the hot baking sheet. Avoid waiting for the entire cookie to turn golden brown, since excessive baking can produce dry, crunchy cookies rather than the desired soft, tender centers. Baking times may vary with cookie size, oven calibration, and baking sheet material.

Step 10: Cool the Cookies Without Drying Them Out. Remove the baking sheet from the oven and allow the sugar cookies to rest on the sheet for approximately 5 minutes. During this resting period, the residual heat helps the centers finish setting while the cookies become firm enough to move without breaking. Carefully transfer them to a wire cooling rack using a thin spatula and allow them to cool completely. The finished cookies should have lightly golden edges, soft centers, a gentle vanilla aroma, and a rich buttery flavor. Let the baking sheet cool before adding another batch of dough, and store any remaining chilled dough in the refrigerator while the first batch bakes.

Step 11: Decorate and Serve Your Homemade Sugar Cookies. Once the cookies have cooled completely, serve them plain to enjoy their classic buttery vanilla flavor or decorate them with a simple powdered-sugar glaze, vanilla buttercream, or colorful sprinkles. For a quick glaze, combine powdered sugar with a little milk and vanilla extract, adjusting the consistency until it can be drizzled or spread easily. Allow any glaze to set before stacking the cookies. These soft sugar cookies are delicious alongside coffee, tea, or a cold glass of milk and make an excellent addition to holiday cookie platters, homemade gift boxes, birthdays, and family celebrations. For the freshest texture, serve them shortly after baking or store them correctly until needed.