Strawberry Whoopee Pies

Cookies:

1 cup (about 5 ounces) stemmed and halved strawberries
3 1/2 cups all-purpose flour
1 1/2 tsp. baking powder
1 tsp. baking soda
3/4 tsp. salt
2 cups light brown sugar
2/3 cup canola oil
1/2 cup plain yogurt
2 large eggs


Filling:

1 cup (about 5 ounces) stemmed and halved strawberries
5 egg whites
1 1/2 cups granulated sugar
4 sticks butter , cut into cubes, at room temperature
Red no-taste gel food coloring


To make cookies: Put strawberries in a food processor and pulse in short bursts just until they are chopped into small pieces (about 4 to 5 pulses), and set aside. (Be careful not to puree them.) Sift flour, baking powder, baking soda, and salt into a medium bowl, and set aside.

Put brown sugar and oil in a large bowl and mix well, using the back of a spoon to break up any lumps in sugar. Whisk in chopped strawberries and yogurt until combined, then whisk in eggs, one at a time, just until combined. Fold in flour mixture in two parts, being careful not to overwork the batter. Cover and refrigerate for 30 minutes.

Preheat oven to 350°. Using a measuring spoon, drop a heaping tablespoon of batter onto a parchment-paper-lined baking sheet to form each cookie, spacing dollops about 2 inches apart. Working in batches, bake until cookies are set and a toothpick inserted in the middle comes out clean, 10 to 12 minutes. Remove cookies from oven; cool completely.

To make filling: Puree strawberries in a food processor until smooth (about 15 seconds); set aside. Whisk egg whites and granulated sugar together in the top of a double boiler until sugar is dissolved and mixture is milky white, about 2 minutes. Transfer egg white mixture to the bowl of an electric mixer fitted with a whisk attachment and whisk on high speed until soft peaks form and mixture is glossy, about 2 minutes. Remove whisk attachment and replace with paddle attachment. Add butter and beat until smooth and fluffy, about 5 minutes. Add reserved strawberry puree and about 3 to 5 drops food coloring (frosting should be a light shade of pink), and beat again until well combined, about 1 minute more.

To assemble: Generously frost the flat side of half of the cookies, then top each with an unfrosted cookie to form sandwiches. Transfer to a platter and serve.