Take the butter out of the refrigerator 30–45 minutes before starting. It should be soft enough to press a finger into easily but not greasy or melting. This prevents overly stiff dough or excessive spreading.

In a large mixing bowl, beat the softened butter, powdered sugar, and granulated sugar together for 2–3 minutes until light, creamy, and slightly fluffy. Use a hand mixer on medium speed or a stand mixer with the paddle attachment, scraping down the sides as needed.

Beat in the vanilla extract and fine sea salt just until combined. If desired, you can add about 1/4 teaspoon almond extract in addition to the vanilla for a slight almond note.

In a separate bowl, whisk together the all-purpose flour and cornstarch until well blended. This helps keep the dough smooth and prevents dry pockets of flour.

Add the dry ingredients to the butter mixture in two additions, mixing on low speed or by hand just until no streaks of flour remain. The dough will look crumbly at first, then start to clump together. Do not overmix or the cookies may turn tough.

If rolling the dough into balls or logs, you may not need any liquid. For piping soft swirls or rings, add 1–2 tablespoons of milk or heavy cream and mix again. The dough should be soft enough to pipe but still hold its shape, similar to thick mashed potatoes.

Cover the bowl and chill the dough in the refrigerator for at least 30 minutes and up to 24 hours. Chilling helps the cookies hold their shape and reduces spreading.

Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats. Do not grease the pans, as extra fat can cause spreading.

Shape the chilled dough using one of these methods: (1) Simple rounds: Scoop about 1 tablespoon of dough, roll into a ball, and flatten slightly with your fingers or the bottom of a glass. (2) Piped butter cookies: Spoon softened dough into a piping bag fitted with a large star tip and pipe rosettes or rings, spacing about 2 inches apart. (3) Slice-and-bake: Roll dough into a log about 2 inches thick, wrap in plastic, chill until firm, then slice into 1/4-inch rounds.

If using, sprinkle shaped cookies with coarse sugar, colored sanding sugar, or press a few sprinkles onto the tops before baking. Leave some plain if you plan to dip or drizzle them with melted chocolate after baking.

Bake one sheet at a time for 10–13 minutes, depending on cookie thickness and your oven. For softer, more shortbread-like cookies, remove when the edges are just barely golden. For crisper, classic butter cookies, bake until the edges are a deeper golden brown. The cookies will firm up as they cool.

Let the cookies cool on the baking sheet for about 5 minutes, then transfer to a wire rack to cool completely. They are fragile when hot.

Once cooled, optionally dip half of each cookie in melted chocolate or drizzle chocolate over the tops. Sprinkle with additional sprinkles, chopped nuts, or sanding sugar if desired. Let the chocolate set, then serve with tea, coffee, or milk.