These Key Lime Sandwich Cookies with Raspberry Buttercream are tangy key lime butter cookies sandwiched with a creamy, fruity raspberry buttercream. They're two treats in one and perfect for your Valentine this year!
In a large bowl, whisk together flour, cornstarch and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream butter and sugar until light and fluffy, about 2 minutes. Add the egg yolks while mixing, scraping down the sides of the bowl when needed. Add the lime zest and lime juice and continue to mix until well combined. Add the flour mixture and mix until just incorporated. Divide the dough into two equal portions and wrap tightly in plastic wrap and chill for one hour.
While the dough is chilling, make your raspberry buttercream. In a clean bowl of your stand mixer, cream butter until smooth and fluffy. Add the raspberry preserves and continue to mix until well blended, Add the sifted confectioners' sugar and pinch of salt and mix on low speed until incorporated. Increase the speed to medium and mix until light and fluffy, about 2 minutes. If buttercream appears too thin, add more confectioners' sugar, too thick, add a teaspoon or so of milk. Remember, you want a firmer buttercream for the sandwich cookie so it doesn't ooze out. Place the buttercream in the fridge while you make the cookies.
Preheat oven to 325 degrees. Line two large baking sheets with parchment paper or a silicone baking mat. Set aside.
Turn one portion of dough out onto a well-floured surface and roll to 1/4-inch thickness. Using a 1 3/4-inch cookie cutter, cut out cookies. Transfer cookies to prepared sheets. Gather up scraps of dough and reroll and cut more cookies. Place the cutouts in the freezer to chill for 15 minutes. Remove from freezer and bake for 13-15 minutes or until lightly browned around the edges, switching trays at midway point. Transfer sheets to wire racks to cool completely.
Repeat with remaining dough in refrigerator. Use sprinkles for this portion of cutouts as they will be the tops of your sandwich cookies.
Once cookies are totally cooled, spread or pipe a dollop of the raspberry buttercream in the center on the flat side of the half of the cookies without the sprinkles. Top with remaining cookies, flat side down, sprinkle side up, and gently press together. Cookies will keep in an airtight container in the refrigerator for 5 days.