For the cake: 

1. Preheat the oven to 350°F. Prepare 3 8-inch round baking pans, line the bottom with parchment paper and grease the sides. Then dust with a light coating of equal parts flour and cocoa powder. 
2. In a large mixing bowl, combine the sugar, vegetable oil, eggs and vanilla extract. Beat on medium speed until the eggs and oil are well incorporated and the batter is lighter in color. Next mix in the sour cream and beat until well combined.
3. In a separate bowl, sift together the dry ingredients. Add half the dry ingredients to the wet ingredients, followed by half of the coffee, and mix until the flour is incorporated at a low speed. Then add the remaining dry ingredients and coffee. Beat until all of the ingredients are well combined. Use a spatula to scrape down the sides of the bowl and stir the batter from the bottom to the top to ensure it’s well mixed.
4. Divide the batter evenly between the three pans, about 1 2/3 cups of batter per pan. Bake at 350°F for 20-24 minutes.  Test the cake for doneness by inserting a toothpick into the center of the cake. If the toothpick comes out clean, the cake is done. Remove from the oven and allow to cool completely.

For the filling: 

1. Chop and puree the strawberries using an immersion blender or food processor.
2. In a medium-sized saucepan, combine pureed strawberries, lemon juice sugar and flour, stir well. Cook over medium-high heat until the mixture starts to boil, stirring frequently.
3. Reduce heat and simmer for another 5 minutes, stirring occasionally until the strawberry puree starts to thicken. If the puree seems to thin, add up to 1 tablespoon of additional flour.
4. Allow the puree to cool completely, refrigerating to help speed up the process.

For the frosting: 

1. Wipe down the inside of your stainless-steel bowl with vinegar to remove any grease. Chop the chocolate bars into smaller pieces, about the size of a nickel, set aside.
2. Combine sugar and egg whites in the bowl with candy thermometer attached. Set the bowl over top of a pot with 1 ¼ cups water covering the bottom. Place over medium heat.
3. Stir constantly with a whisk until the mixture reaches 140°-160°  The sugar should be dissolved in the egg whites. You can test this by placing a drop on your fingertips and rubbing them together. The mixture should be completely smooth.
4. In a microwave-safe bowl, microwave the chocolate 50% power in 30-second increments, stirring each time until the chocolate is melted and smooth. Set aside to cool.
5. Immediately place the mixing bowl on your stand. Using the wire whisk attachment, beat the eggs white on low for 2 minutes then increase to medium-high. Beat for another 5 minutes. At this point, the egg whites should have turned white and the body of the meringue starts to form. Increase the mixing speed to high. It will start to look glossy as the peaks begin to form. Beat for another 5-8 minutes until the bottom of your bowl is cool to the touch and your meringue has stiff peaks.
6. Turn your mixer down to medium-low. Slowly add the butter, 1 tbsp at a time. As you add more butter, the frosting might appear to have curdled and lost its body, that’s ok. Scrape down the sides of the bowl.
7. Switch to the paddle attachment, add the vanilla extract and continue beating on medium-high speed until the buttercream comes together. Slowly drizzle in the chocolate and continue beating until stiff peaks form, about 3-5 minutes.

Assemble

1. Level off the cakes by removing any domes. Place a dollop of frosting on a cake board and place the bottom layer of cake over that.
2. Pipe a thick border (a dam) along the outside edge of the layer. You may need to do this twice. Spread half of the strawberry mixture over the cake, carefully filling the inside of the dam. Pipe another thin layer of frosting over the strawberry sauce and spread evenly with your offset spatula.
3. Add the second layer of cake and repeat the above steps using all of the remaining strawberry sauce. Then, add the final layer of cake on top.
4. Use a piping bag to fill in any gaps between the layers, then use an offset spatula to create a thin crumb coat around the outside and top of the cake. Chill for 15 minutes. 
5. Proceed to frost the top and sides of the cake using an offset spatula. Once fully frosted, run the spatula around the outside edge of the cake while turning the turntable to create the indent in the frosting.
6. Use the remaining frosting to pipe the florets on the top of the cake using an Ateco 846 tip (large open star). Garnish with strawberries if desired.