Whisk the flour, baking powder, and salt together in a medium bowl. Set aside.

In a large bowl using a hand mixer or a stand mixer fitted with a paddle attachment, beat the butter and granulated sugar together on medium-high speed until creamed, about 2 minutes. Add the egg, egg yolk, and vanilla extract and beat on high speed until combined, about 1 minute. Scrape down the sides and up the bottom of the bowl and beat again as needed to combine.

Add the dry ingredients to the wet ingredients and mix on low until combined. Dough will be thick and sticky. Remove from the mixing bowl. No need to rinse out the mixing bowl.

There’s about 30 ounces of dough (1 lb, 14 ounces). Divide into three equal portions, about 10 ounces each. One portion is your vanilla dough. Nothing will be added to it. Set vanilla dough aside. The other two portions will be your strawberry dough and chocolate dough.

Place one portion of dough back into the mixing bowl. Add all of the strawberry dough ingredients. I recommend starting with 1 drop of red or pink food coloring. Beat on low speed until dough is combined. Add another drop or 2 of food coloring until you reach the pink color desired. For the pictured cookies, I only used 1 drop of dusty rose gel food coloring. Remove from the mixing bowl. No need to rinse out the mixing bowl.

Place last portion of dough back into the mixing bowl. Add all of the chocolate dough ingredients. Beat on low speed until dough is combined.

See step-by-step photos above showing this following step so you have a better understanding. Line a 9×5-inch loaf pan with aluminum foil or parchment paper, leaving an overhang on the sides to lift the chilled cookie dough out. I recommend layering the cookie dough into the pan in the following order: strawberry dough on the bottom, vanilla dough in the middle, chocolate dough on top. Using your hands, press each dough layer firmly and evenly into prepared loaf pan.

Cover loaf pan tightly and chill dough in the refrigerator for at least 3 hours (and up to 4 days) or 1 hour in the freezer. (See make ahead tip if you wish to freeze longer.)

Preheat oven to 350°F (177°C). Line 2 baking sheets with parchment paper or silicone baking mats. Set aside.

Lift dough out of the pan using the overhang of parchment paper on the sides. You’ll have a 9×5-inch block of dough. Slice in half lengthwise so you have two 2.5 x 9-inch rectangles. Use a sharp knife to trim off the ends so the rectangles are 8 inches long. Slice each into 16 cookies. Each cookie is 1/2 inch thick. Trim the cookie edges to make neat rectangles, if desired.*

Arrange cookies 2-3 inches apart on the baking sheets. If desired, brush each lightly with egg wash (see recipe note) and sprinkle with coarse sugar. Bake for 11-13 minutes or until lightly browned around the edges.

Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Once cool, enjoy cookies or dip in melted chocolate. See recipe note.

Cookies without chocolate coating will stay fresh covered at room temperature for 1 week. Cookies with chocolate coating will stay fresh covered at room temperature for 3 days or in the refrigerator for 1 week.