Start the strawberry reduction by adding the sliced strawberries into a food processor and pulse until you have about 1 ½ cups puree.
Add the puree into a medium saucepan and heat over medium-high heat, stirring often, until thickened and reduced by about half. This should take about 20 minutes.
Set the reduction aside to cool.
Preheat your oven to 350°F (180°C), or 160°C if using a fan oven. and prepare three 8-inch (20 cm) cake pans by spraying generously with non-stick spray and place a round of parchment paper in the bottom of each pan.
In a medium bowl, add the sour cream, milk, eggs, vanilla, and cooled puree. Whisk to combine and set aside.
In the bowl of a stand mixer equipped with a whisk attachment, add the flour, sugar, baking powder, and baking soda. Whisk to combine.
Slowly add the room temperature butter into the dry ingredients 1 tablespoon at a time. Once all the butter is combined, the flour should have a sand-like texture.
With the mixer on low speed, slowly pour half of the wet ingredients into the flour mixture. Mix until combined.
Add the remaining wet ingredients and mix until just combined. Scrape the sides and bottom of the bowl and mix additionally if needed.
Divide the batter evenly between the three prepared cake pans and gently tap on the pans on the counter to release any air bubbles.
Bake for 25-27 minutes or until a toothpick inserted in the center of each cake comes out clean.
Remove the cakes from the oven and allow to cool for five minutes, then flip the cakes onto a wire rack to cool completely.