Preheat the oven to 350°F (175°C). Grease two 9-inch pans with butter, dust with flour, and line the bottoms with parchment paper. This ensures the cakes release smoothly after baking. Double-coating pans like this prevents breakage and gives you neat edges.
Cream the butter and sugar in a large mixing bowl for about 4–5 minutes until pale and fluffy. This step builds air into the mixture, giving the cake its light texture. Add eggs one by one, mixing well after each, followed by vanilla extract. This prevents curdling and ensures everything blends evenly.
In a separate bowl, whisk flour, baking powder, and salt. In another cup, combine milk, lemon juice, and zest. Add the flour mixture and milk mixture alternately into the butter mixture, starting and ending with flour. Mix gently and only until combined, as overmixing makes the cake dense.
Take the diced strawberries that were coated with flour and gently fold them into the batter using a spatula. The flour coating helps them stay evenly spread without sinking to the bottom. Be careful not to crush the berries, as this will release excess juice.
Divide the batter evenly into the prepared pans. Bake for 30–35 minutes until a toothpick inserted in the center comes out with only a few crumbs. Let the cakes cool in the pans for 10 minutes, then transfer to wire racks to cool completely. Cooling prevents the frosting from melting later.
Beat softened butter until creamy, then gradually add powdered sugar. Mix in strawberry puree, lemon juice, zest, and vanilla extract until smooth. Add food coloring if desired. Spread frosting between cake layers, over the top, and around the sides. Decorate with strawberries, lemon slices, and mint.