These classic Butter Cookies are crisp around the edges, tender in the center, and packed with rich buttery vanilla flavor. Pipe the soft dough into beautiful swirls for an easy homemade version of those classic Danish butter cookies everyone loves.
Preheat oven to 350°F. Line two light-colored baking sheets with parchment paper.
Add very soft butter and granulated sugar to the bowl of a stand mixer. Cream with the paddle attachment until light and fluffy, about 2–3 minutes.
Mix in egg yolk and vanilla, scraping the sides of the bowl as needed.
Add flour and cornstarch and mix on low just until combined.
Mix in milk, 1 tablespoon at a time, until the dough is soft enough to pipe but still thick enough to hold its shape.
Transfer dough to a piping bag fitted with a large open-star tip. Pipe 2-inch swirls onto prepared baking sheets, leaving about 1 inch between cookies. Top with coarse sugar, if desired.
Refrigerate the piped cookies for 20–30 minutes to help them hold their shape.
Bake for 10–13 minutes, or until the edges are just beginning to turn lightly golden.
Cool on the baking sheet for 5 minutes before transferring to a cooling rack.
Notes
The butter should be very soft but not melted. If it's too cold, the dough will be difficult to pipe.
Add only as much milk as needed to make the dough pipeable. Too much can cause the cookies to spread.
Chilling the piped dough helps preserve those pretty ridges.
Don't overbake. Look for pale centers with lightly golden edges.
Dip cooled cookies halfway in melted chocolate for a chocolate butter cookie variation.