Start by pureeing 3/4 lbs of fresh strawberries with a food processor. Afterwards, you should be left with about 1 cup of puree. Place the strawberry puree into a saucepan over medium-low heat and simmer for 20-25 minutes, stirring occasionally. When you’re done with the reduction, you should have about 1/2 cup (if you have more, keep cooking!). Place the reduced puree into an airtight container and refrigerate it for at least 30 minutes, or until it reaches room temperature. Then, whisk it together with the whole milk and set aside.
Preheat the oven to 350ºF and prepare three 6-inch or two 9-inch cake pans by spraying the sides with cooking spray and fitting the bottoms with wax or parchment paper circles. In a medium sized bowl, place the sifted cake flour, baking powder, baking soda, and salt and whisk to combine.
In the bowl of your stand mixer with the paddle attachment, whip the butter on high for one minute. Scrape down the paddle and bowl, add the granulated sugar, and beat on high for another 2 minutes. Turn the mixer to low and add the eggs one at a time, making sure each one is incorporated before adding the next, then turn the mixer to high and beat for 1 minute.
Turn the mixer to low and add the vanilla and sour cream until incorporated. Keeping the mixer on low, add all of the dry ingredients at once until just combined, then add the strawberry milk mixture and pink food coloring (if using) until just combined, about 30 seconds. Give the batter a few stirs by hand to make sure everything is incorporated without over-mixing. Pour the batter into the prepared cake pans, about 2/3 full.
Bake the cakes for 30-35 minutes, until a toothpick inserted comes out clean. Cool the cakes in the pan for five minutes, after which you can turn them out and continue to cool them on a wire rack or sheet pan for several hours.