¾teaspoonalmond extractoptional, but highly recommended
¾cupmilkpreferably whole or 2%
1 1/2cupsunsalted buttersoftened to cool room temperature
5cupspowdered sugarplus more, if needed
1-2tablespoonshalf & half, cream or milk
2teaspoonspure vanilla extract
1/2teaspoonalmond extractoptional, but highly recommended
1pound (approx)fresh strawberriessliced or chopped
Preheat oven to 350°F with a rack placed in the center.
In a medium bowl, whisk flour, baking powder and salt until combined. Set aside.
Using a stand mixer fitted with the paddle attachment (preferred) or a hand mixer, beat sugar, oil, eggs, egg whites, and extracts until fully combined (about one full minute). Add the sour cream and beat until combined. Add half of the flour mixture, beating until just combined. While still beating, slowly add milk, then the remaining flour mixture, scraping the sides and bottom of the bowl as needed. Mix the batter fully, but be careful not to overmix it.
Pour the batter into a greased 9x13 baking pan (see note). Tap the pan on the countertop a couple times to remove any air bubbles. Bake for 25-30 minutes, until a toothpick inserted into the center comes out clean. If necessary, rotate the pan once during bake time to ensure even browning. Place the pan on a rack to cool completely.
Using a hand mixer, or stand mixer fitted with the paddle attachment, beat butter and 2 cups of the powdered sugar until well-combined. Continue to add remaining powdered sugar one cup at a time (starting out the mixer low and increasing to medium-high). Add extracts, 1 tablespoon milk and salt, beat until well combined. Add more milk, if necessary. Turn the mixer to medium-high and beat well for 1-2 minutes. Note: Depending on how thick you want the frosting, you can easily adjust the consistency by adding more powdered sugar (to thicken) or more milk (to thin).
Using about 1/3 of the frosting, spread an even layer over the top of the cake. Place remaining frosting in a piping bag fitted with your desired tip (I used a star tip).
Pipe a border around the perimeter of the cake. Place the blueberries in the upper left corner to form the "star" portion of the flag. Alternate rows of strawberries and piped frosting for the stripes.
Pan sizes: This cake can also be baked in a 10x15x1 "jelly roll" pan (as pictured). Note: The cake will rise all the way to the top of the jelly roll pan. Be careful not to overmeasure the ingredients when preparing the batter. Bake the 10x15x1 cake for 18-23 minutes, until a toothpick inserted into the center comes out clean.Tip: If your strawberries are not very sweet and juicy, you can toss them with a little sugar or some strawberry jam (thin it out in the microwave for a few seconds). This will make them extra juicy and glossy.