Pre-heat oven to 350 degrees.
Cream butter and sugar in the bowl of a stand mixer or in a bowl with a hand mixer, until light and fluffy.
In a separate medium-sized bowl, whisk flour, baking flour, and salt together.
Slowly mix the dry ingredients into the butter and sugar mixture, alternating with milk. Add vanilla and mix until just blended. The batter will be thick.
In a separate large bowl, whisk egg whites with a hand mixer until stiff peaks form.
Gently fold whipped egg whites, chopped strawberries, and red food coloring (if using) into the batter until just blended.
Line a cupcake pan with paper liners and divide batter evenly among liners, filling each about ¾ of the way full.
Bake at 350 degrees for about 16-18 minutes, until a toothpick comes out clean.
After cooling in the pan for a few minutes, move cupcakes to wire rack to cool completely.
Once cupcakes are cooled, use a cupcake corer or small knife to remove the center of the cupcake.
Spoon about 2 teaspoons of chocolate ganache into each cupcake. You should have enough ganache left to top cupcakes.
Fill a pastry bag with buttercream icing and using a #2A pastry tip, pipe buttercream around cupcake.
Drizzle the remaining chocolate ganache over the buttercream, letting it drip down the sides. If ganache has hardened, place back in microwave at 50% power for 30 second intervals
Sprinkle rainbow sprinkles over the top of each cupcake.