Prep oven and pan. Preheat the oven to 350°F (180°C). Like baking sheets with parchment paper. You can also chill the dough overnight (for best results for thicker, chewier cookies.)
Combine dry ingredients. Whisk together flour, cornstarch, baking soda, and salt in small bowl. 2 ¼ cups (280 g) all purpose flour 1 ½ teaspoons cornstarch ¾ teaspoon salt 1 teaspoon baking soda
Cream butter and sugar. In a bowl of a stand mixer fitted with a paddle attachment beat together butter and granulated sugar on medium speed until light and fluffy, about 2 minutes. ¾ cup (170 g) unsalted butter 1 ¼ cups (250 g) granulated sugar
Add vanilla and eggs. Add egg and egg yolk, one at a time whisking to combine. Add vanilla and mix just until combined. 1 large egg 1 large egg yolk 2 teaspoons vanilla extract
Add dry ingredients. Gradually stir in flour mixture with a wooden spoon or spatula until just combined.
Divide dough. Divide dough into 3 equal portions (about 250 g) each. In one bowl stir in the freeze dried strawberries until fully incorporated and dough is pink. In a second bowl stir in the cocoa powder until fully incorporated and dough is brown. Leave one bowl as is. ¼ cup freeze-dried strawberry powder 1 Tablespoon Dutch process cocoa powder
Scoop the cookies. Using a tablespoon, scoop each portion of the dough and roll into balls. Press together one vanilla, one strawberry, one chocolate together and roll into a ball again. Because of the strawberry powder you may have a little extra strawberry dough compared to the other three doughs. You can just bake that into an extra cookie! Roll in granulated sugar. Place cookies onto prepared cookie sheets about 2 inches apart. Cookies will be a bit larger, so bake only 6-8 cookies at a time to allow for cookies to spread.
Bake and cool cookies. Bake the cookie sheet on the middle rack for 10-12 minutes, until edges are set and centers are slightly puffed. Remove from the oven and let cool on a baking sheet for 5 minutes before transferring to a wire rack to cool completely.