Preheat oven to 350°F (175°C). Grease and flour three 9-inch round cake pans or line with parchment paper.
In a large mixing bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt until well combined.
Add milk, vegetable oil, eggs, and vanilla. Mix until the batter is smooth and uniform.
Carefully add the boiling water and mix on high speed for 1 minute. The batter will be thin, but this creates a moist cake.
Divide batter evenly between the prepared pans and smooth the tops.
Bake for 30–35 minutes or until a toothpick inserted into the center comes out clean.
Cool cakes in pans for 10 minutes, then remove and let cool completely on wire racks.
2. Make the Strawberry Buttercream:
In a large bowl, beat softened butter with an electric mixer until light and creamy (about 2–3 minutes).
Gradually add powdered sugar, one cup at a time, beating well after each addition.
Mix in the strawberry puree and vanilla extract. Continue beating until the frosting is smooth, fluffy, and pale pink. If too soft, add more powdered sugar; if too thick, add a bit more puree or a splash of milk.
