Chocolate Chip Cookie Cake

For the cake - Preheat the oven to 350°F: Grease a 9-inch round cake pan with butter. Dust the pan lightly with flour, then tap out any excess.

For the cake - Combine the dry ingredients: In a medium bowl, add the flour and baking soda. Whisk until combined.

For the cake - Beat the butter, brown sugar, vanilla, and salt: In the bowl of a stand mixer with the paddle attachment or in a large mixing bowl with a hand mixer, beat together the butter, brown sugar, vanilla extract, and salt on medium-high speed until pale and fluffy, about 2 minutes.

For the cake - Add the egg: Add the egg and beat until fully combined. Scrape down the bottom and sides of the bowl with a rubber spatula.

For the cake - Add the dry ingredients: Beat in the flour mixture on low speed, or gently fold it in with a rubber spatula, just until combined and no streaks of flour remain.

For the cake - Stir in the chocolate chips: Stir in the chocolate chips with a rubber spatula until evenly distributed.

For the cake - Bake: Press the dough into the prepared cake pan and use a rubber spatula or an offset spatula to smooth out the dough into an even layer. Bake for 20 to 25 minutes, or until a toothpick inserted in the center comes out clean.

For the cake - Cool: Let the cake cool completely in the pan on a wire rack.

For the chocolate frosting - Melt the chocolate for the frosting: Place chocolate chips in a medium microwave-safe bowl and microwave in 30-second bursts until melted and smooth, stirring with a rubber spatula or spoon after each burst. Set aside to cool.

For the chocolate frosting - Cream the butter: To make the frosting: In a stand mixer fitted with the paddle attachment, or in a large mixing bowl with a hand mixer, beat the butter on medium speed until smooth and creamy, about 2 minutes.

For the chocolate frosting - Add the powdered sugar and vanilla: Add the powdered sugar and vanilla extract and continue beating on medium speed until combined and smooth, about 2 minutes.

For the chocolate frosting - Add the chocolate: Pour in the melted and cooled chocolate and beat on medium speed until uniform in color and silky. Pause and scrape the bottom and sides of the bowl with a rubber spatula as needed.

For the chocolate frosting - Fill a piping bag with frosting and pipe onto cake: Use a butter knife to loosen the cake from the sides of the pan and carefully transfer the cake to a serving dish, or you can serve it directly from the pan instead. Fill a piping bag fitted with a large star tip with the chocolate frosting. Pipe rosettes of frosting along the edge of the chocolate chip cookie cake. Decorate with sprinkles.

For the chocolate frosting - Serve: For neater slices after decorating, let the cookie cake sit a bit before you cut it. The finished chocolate chip cookie cake will keep for up to 3 days, covered, at room temperature.