Prep pans and oven (10 minutes).
Preheat oven to 350°F (175°C). Grease and line two 9-inch round cake pans with parchment.
Make strawberry puree (20 minutes).
Puree fresh strawberries, then simmer in a saucepan until reduced to about 1 cup. Let cool completely.
Mix dry ingredients (3 minutes).
Whisk together flour, baking powder, baking soda, and salt.
Cream butter and sugar (5 minutes).
In the bowl of a stand mixer (or with a hand mixer), beat butter and sugar until light and fluffy.
Add eggs and vanilla (3 minutes).
Beat in eggs one at a time, then stir in vanilla extract.
Add sour cream and milk (2 minutes).
Mix until just combined—this adds moisture and tenderness.
Combine wet and dry (2 minutes).
Add flour mixture in thirds, alternating with milk, mixing gently after each addition.
Add cooled strawberry puree (1 minute).
Fold in until evenly combined and the batter is a soft pink.
Bake (30–35 minutes).
Divide batter between prepared pans. Bake until a toothpick comes out clean.
Cool completely (30 minutes).
Let cakes rest in pans for 10 minutes, then transfer to wire racks.
Make strawberry buttercream (10 minutes).
Beat butter until creamy, then add strawberry powder, powdered sugar, vanilla, and cream. Beat until fluffy.
Assemble and frost (15 minutes).
Spread frosting between layers, then frost the outside. Decorate with fresh strawberries.