So you aren't trying to make all of this in one day, it might be easier to make this sauce the day before you plan to make the cake. Puree 2 cups of chopped strawberries in a blender or food processor and add the puree to a medium saucepan over medium heat. Bring the puree to a simmer and reduce the heat slightly to medium low. Simmer, stirring frequently, until it becomes a jelly-like consistency. You can do other things during this time, just don't stray too far from the stove because you'll need to stir this a lot.

Spray a 9x13 rectangle pan with nonstick spray and preheat the oven to 350 degrees.

In one bowl, combine flour and baking soda. Whisk together and set aside.

In another bowl, beat butter on medium-high speed with an electric mixer until smooth and creamy. Add sugar and mix until combined and fluffy. Next add the egg, egg white, and vanilla, and mix well on medium speed. Then add the strawberry sauce and mix until combined.

Next add half of the flour mixture and half of the buttermilk. Mix on low until just combined. Add the second half of the flour and buttermilk and mix until completely combined.

Pour the batter into the prepared pan and bake for 20 minutes. Let the cake cool in the pan for 10 minutes, then let it cool completely on a wire rack.

When the cake is cool, transfer it to a sheet of parchment paper and cut out the circles, which will become the small cake layers. I used a large cup for this, but you can use whatever you have. My cake layers ended up being about 4 inches in diameter.

In a medium-sized bow, beat butter with an electric mixer on medium-high speed until smooth and creamy. Add the vanilla and strawberry sauce and mix well. Next add half of the powdered sugar and mix on low speed until mostly combined. Then add the rest of the powdered sugar and mix on medium speed for one minute.

Place a mini cake layer on a small cake stand or plate. Spread frosting between each of the layers and around the outside of the cake. I had enough left over to pipe some little borders. Garnish with strawberries or a little strawberry heart.