Make the Reduced Strawberry Purèe: Using a food processor, purèe the chopped strawberries (you’ll end up with about ½ Cup after this). Add the strawberry purèe into a small saucepan set over medium heat. Bring to a boil, then reduce the heat to low and simmer for 10-15 minutes, until it becomes jam-like and has reduced by half. You’ll end up with about ¼ Cup of reduced purèe after this step. Let it cool completely to room temperature (either in the refrigerator or on the counter) before moving on in the recipe.
Make the Strawberry Buttercream: With a hand mixer or paddle attachment on your stand mixer, beat the butter on medium-high until it’s creamy, about 5 minutes. Add the powdered sugar about a cup at a time and mix on low speed, making sure each addition is fully incorporated before adding the next. Scrape down the bowl and paddle as needed. Add the (room temperature!) reduced strawberry purèe and a pinch of salt. Continue mixing on low speed until fully incorporated and smooth, scraping down the bowl and paddle as needed, 1-2 minutes.
