Patriotic Poke Cake

FOR THE WHITE CAKE: Adjust oven rack to middle position and heat oven to 350 degrees. Grease two 9-inch cake pans, line with parchment paper, grease parchment, and flour pans.

Mix milk, egg whites, and vanilla together in 2-cup liquid measuring cup. Using stand mixer fitted with paddle attachment, mix flour, sugar, baking powder, and salt on low speed until combined, about 5 seconds. Add butter, 1 piece at a time, and mix until only pea-size pieces remain, about 1 minute.

Add half of milk mixture, increase speed to medium-high, and beat until light and fluffy, about 30 seconds. Reduce speed to medium-low, add remaining milk mixture, and beat until incorporated, about 15 seconds (batter may look slightly curdled). Give batter final stir by hand; do not overmix.

Divide batter evenly between prepared pans and smooth tops with rubber spatula. Bake until tops are light golden and toothpick inserted in center comes out clean, 23 to 25 minutes, switching and rotating pans halfway through baking. Let cakes cool completely in pans on wire rack, about 2 hours.

FOR THE BLUEBERRY AND STRAWBERRY SYRUPS: Cook blueberries, ¾ cup water, and 2 tablespoons sugar in medium saucepan over medium-low heat, covered, until blueberries are softened, about 8 minutes. Strain through fine-mesh strainer into medium bowl; discard solids. Whisk berry-flavored gelatin into juices and cool slightly, about 15 minutes. Repeat cooking and straining using strawberries, remaining ½ cup water, and remaining 2 tablespoons sugar. Whisk strawberry-flavored gelatin into juices and cool slightly, about 15 minutes.

FOR THE LIGHTLY SWEETENED WHIPPED CREAM: Using stand mixer fitted with whisk attachment, whip cream, sugar, and vanilla on medium-low speed until foamy, about 1 minute. Increase speed to high and whip until stiff peaks form, 1 to 3 minutes. Set aside.

TO ASSEMBLE: Using skewer, poke 25 holes in top of each cake, twisting gently to form slightly larger holes. Pour cooled blueberry syrup over 1 cake layer. Repeat with cooled strawberry syrup and second cake layer. Cover cakes with plastic wrap and refrigerate until gelatin is set, at least 3 hours or up to 24 hours. Run knife along interior of pans. Invert blueberry cake onto wire rack, then flip cake right side up onto serving platter. Spread 1 cup whipped cream over top. Invert strawberry cake and place, right side up, on whipped cream. Spread remaining whipped cream over top and sides of cake. Slice and serve.