Make the Strawberry Reduction: 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 30-35 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 a 13x9 inch cake pan or casserole dish by spraying the sides with cooking spray and lining the bottom with parchment paper.
In a medium bowl, add the sifted cake flour, baking powder, baking soda, and salt. Whisk to combine and set aside.
In the bowl of your stand mixer with the paddle attachment, whip the butter on high until creamy, 2 minutes. Add the granulated sugar and beat together with the butter at medium speed for 2 minutes, until light and fluffy. Turn the mixer to low and add the eggs one at a time, making sure each one is incorporated before adding the next. Add the vanilla and sour cream, then turn the mixer to high and beat for 1 minute.
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 pan and use a spatula to smooth the batter down evenly and spread it into all four corners.
Bake the cake for 35-40 minutes, until a toothpick inserted comes out with just a few moist crumbs. Let the cake cool completely before frosting.