In a medium saucepan, combine frozen strawberries, granulated sugar, brown sugar, 4 tablespoons of water, and lemon juice. Heat over medium heat, stirring occasionally, until the berries begin to break down and release their juices — about 8–10 minutes.

Mix 1 tablespoon cornstarch with 1 tablespoon water to make a slurry. Stir it into the simmering strawberry mixture. Cook another 2–3 minutes until thickened. Remove from heat, let cool completely, then refrigerate.

Set your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans. Optionally line the bottoms with parchment paper for easier release.

In a small bowl, mix cocoa powder with buttermilk until smooth. In a separate large bowl, cream the butter and granulated sugar together with an electric mixer on medium speed until light and fluffy (about 3–4 minutes). Add eggs one at a time, mixing well after each.

In another bowl, whisk together flour, baking powder, baking soda, and salt.

Add the cocoa-buttermilk mixture to the creamed butter and sugar. Mix to combine. Gradually add dry ingredients, alternating with the hot water. Start and end with dry ingredients. Mix until the batter is smooth but don’t overmix.

Divide the batter evenly between the two prepared cake pans. Bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean. Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

In a large bowl or stand mixer, beat the butter until smooth and creamy (about 2–3 minutes). Add freeze-dried strawberry powder, vanilla, salt, and lemon juice. Mix on low to combine.

Gradually add powdered sugar one cup at a time, mixing well and scraping down sides. Add heavy cream a bit at a time, whipping the frosting until light and fluffy. Adjust thickness with more cream or sugar if needed.

If your cakes domed on top, level them with a serrated knife. Place one cake layer on a serving plate or cake board. Pipe a border of buttercream around the edge and fill the center with the chilled strawberry filling.

Add the second cake layer. Apply a thin crumb coat of buttercream and refrigerate for 20–30 minutes. Then apply the final, thicker layer of frosting. Smooth with a spatula or cake scraper.

Decorate with fresh strawberries, chocolate drizzle, or freeze-dried strawberries if desired. Slice and serve. Refrigerate leftovers in an airtight container.