Grease the sides of three 8-inch cake pans and line the bottoms with parchment paper. Preheat then oven to 350 F/180 C.
Combine the cake flour, sugar, cocoa powder, brown sugar, baking powder, baking soda, and salt. Mix in the butter until it resembles coarse sand, about 3 minutes on low speed.
Whisk together the sour cream, milk, eggs, oil, and vanilla. Add half to the bowl and mix on low speed for 1 minute, forming a thick paste. Scrape down the bowl. Mix in the rest of the milk mixture until just combined. Scrape down the bowl. Then mix in the hot coffee until just combined. Scrape the bowl again if needed.
Evenly distribute the cake batter into the prepared cake pans (490 grams in each). Bake for 18-25 minutes, or until a toothpick inserted into the center comes out covered in a few moist crumbs.
For the Filling
Cook the strawberries, water, and lemon juice over medium heat, mashing occasionally, until glossy and thickened, about 15 minutes. Set aside a heaping 1/4 cup for the buttercream.
Mix the sugar and brown sugar into the pot and continue cooking for 3-4 minutes. Stir in the cornstarch slurry and cook 2 minutes longer until it no longer looks cloudy. Transfer the filling to a bowl and set it aside to cool.
For the Buttercream
Cream the butter in a stand mixing bowl until smooth. Then mix in the powdered sugar. Once combined, beat the buttercream for 2-3 minutes until light and fluffy. Mix in the strawberry compote 1 tablespoon at a time, beating well after each addition before adding the next. Then mix in the vanilla extract and heavy cream. Beat the buttercream on medium speed for another 2-3 minutes until light and fluffy again.
Assembly
Pipe a border of strawberry buttercream around the edge of the first cake layer. Then spread half of the strawberry filling in the center.
Continue assembling, with the last cake layer placed upside down for a flat top. Use the remaining buttercream to cover the top and sides of the cake with a thin layer of frosting (for a naked cake look). Then chill the cake in the fridge while you make the ganache. If you prefer a thicker layer of frosting, you will want to make a double batch of buttercream!
Heat the cream in the microwave or in a pot on the stove until almost boiling. Pour the cream over the chocolate chips, then stir to emulsify. Set it aside for 5 minutes to cool. If it’s warm it will melt the buttercream!
Pour the ganache on top of the cake and use an offset spatula to push it over the edges. Let it set for 15 minutes before garnishing the top with whole strawberries and chocolate pieces. Let it set completely at room temperature before chilling to avoid cracking!
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Notes
*Measure your dry ingredients properly. This is my #1 baking tip! Do not ever scoop a measuring cup into your flour as this always leads to using too much flour. Instead, use the spoon-level method. This means fluffing the flour first, then spooning it into your measuring cup/spoon. For the BEST results, use a kitchen scale!*Storage: To keep the cake moist, wrap any leftover cake slices with plastic wrap and store them in an airtight container in the fridge for up to 5 days. You can also store the entire uncut cake in the fridge for up to 1 week!Freezer: You can store the whole, uncut cake or as individual slices wrapped in plastic wrap and stored in an airtight container.Make ahead: Cake layers: Wrap in plastic and refrigerate for 3-5 days or freeze for up to 1 month. Buttercream: Can be made and refrigerated for 1-2 weeks. Strawberry filling: Store in an airtight container in the fridge for 1 week.