Cookies:

In a large mixing bowl or the bowl of a stand mixer, whip the butter until smooth and creamy.

Add the granulated sugar and mix on medium-high speed until well-combined.

Add the milk, vanilla extract, kosher salt, and egg, and mix until well-combined.

Sift in the flour. Use a rubber spatula to gently fold the flour into the butter mixture, periodically scraping the sides of the bowl until all flour has been incorporated. Do not overmix. The mixture will resemble a thick, sticky paste.

Divide the batter into three equal portions, placing each in a separate bowl. To one bowl, add the pink gel food coloring and stir until evenly distributed. Stir the cocoa powder into the second bowl, along with a teaspoon of milk if the mixture seems too dry.

Transfer each color batter to a separate piping bag.

Unroll about 18 inches of plastic wrap/clingfilm on a flat surface. Pipe stripes of batter up and down, continuing until all of the batter has been piped. When done, you should have thick columns of white, brown, and pink batter. (Don’t worry if these arent pretty or perfectly even, you won’t see them anyway!)

Gently roll the plastic wrap from one side to the other, wrapping the colors around each other and creating a tube of batter. For sturdiness, wrap 2-3 additional layers of plastic around the tube.

Place the tube inside a piping bag fitted with a large star tip. (If the tube is longer than the piping bag, you can cut it in half and pipe the cookies in two separate batches.)

Pipe 1 1/2-inch rosettes (or other shape of choice) onto trays lined with silicone baking mats, allowing space in between for the cookies to spread slightly as they bake.

Transfer trays to the refrigerator to chill for 30 minutes. Meanwhile, preheat the oven to 350° F / 175° C.

Bake cookies in preheated oven for 13-15 minutes, or until white cookie dough starts to brown lightly around the edges. Cool on trays for 5 minutes, then transfer to a wire rack to cool completely before filling with buttercream.

Buttercream:

In a large mixing bowl or the bowl of a stand mixer, whip butter until creamy.

Gradually add the confectioner’s sugar, alternating with the whole milk. Continue mixing on medium-high speed until sugar is fully incorporated, scraping down the sides of the bowl with a rubber spatula as needed. Mix in the kosher salt.

Divide the buttercream into three bowls.

Add the cocoa powder to one bowl, the freeze-dried strawberries to the second, and the vanilla bean paste to the third, stirring each until fully incorporated.

Transfer each of the buttercreams into a separate piping bag.

Just as you did with the batter, unroll about 18 inches of plastic wrap/clingfilm on a flat surface. Pipe stripes of buttercream up and down, continuing until all of the buttercream has been piped. When done, you should have thick columns of white, brown, and pink buttercream.

Gently roll the plastic wrap from one side to the other, wrapping the colors around each other and creating a tube of buttercream. For sturdiness, wrap 2-3 additional layers of plastic wrap around the tube.

Place the tube inside a piping bag fitted with a large star tip. (If the tube is longer than the piping bag, you can cut it in half and pipe the buttercream in two separate batches.)

Assembly:

Pair the cookies by size. You should have a total of 12 pairs.

To one half of each pair, pipe a generous swirl of buttercream on the flat side.

Sandwich with the remaining cookies.

Neapolitan buttercream cookies are best enjoyed on the day they are made. Store leftovers in an airtight container at room temperature for up to three days. Leftover cookies can also be frozen in an airtight container.