Preheat oven to 350F (180C). Grease with butter and dust with flour two 9 inch (23 cm) round cake pans.
In a large bowl whisk together the flour, cocoa powder, baking soda and salt.
In another bowl mix sugar with eggs and oil until combined. Mix in buttermilk and vanilla extract. Incorporate flour mixture until well combined. Add hot coffee and mix to combine.

The batter will have a runny consistency.
Pour the batter evenly into the prepared pans.
Bake for about 30-35 minutes until a toothpick inserted into the center comes out clean or with few crumbs attached.
Let pans cool on a cooling rack for 10-15 minutes.

Remove the cakes from the pan and let them cool completely.
Prepare the Chocolate Mousse Frosting. Place the chocolate and 1&1/4 cup cream into a small sauce pan. Place over very low heat until chocolate is melted. Stir in cocoa powder then remove from heat. Meanwhile dissolve gelatin in water and let it swell for about 5 to 10 minutes. Place the gelatin over low heat just until the gelatin dissolves and pour it over the melted chocolate mixture. Let cool completely.

Start with the side of the cake. To make the rose, start in the center, then move your tip in a circle around the center point, once or twice depending on how big you want the rose to be. When the side of the cake is filled with roses continue with the top. Fill any remaining gaps with some frosting.
Refrigerate until ready to serve.