Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking pan with baking spray and line the bottom with parchment paper. Set aside.

In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt until fully combined.

In a separate bowl, whisk together the buttermilk, vegetable oil, sour cream, eggs, and vanilla extract. Slowly incorporate the hot coffee, whisking until blended.

Gradually add the wet ingredients into the dry mixture. Whisk for approximately 1 minute until smooth and uniform.

Pour the batter into the prepared pan. Bake for 27 to 30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Allow the cake to cool in the pan for 30 minutes, then transfer to a wire rack to cool completely. Peel away the parchment paper. Once cooled, slice the cake in half horizontally.

In a chilled mixing bowl, whip the heavy cream until stiff peaks form. Gradually add the vanilla extract and powdered sugar, continuing to whip until firm.

In a microwave-safe bowl, heat the chocolate chips and heavy cream in 30-second intervals until melted and smooth. Allow the mixture to cool for 15 minutes. In another bowl, beat the butter until light and fluffy. Add the vanilla extract and salt. Gradually incorporate the powdered sugar and cocoa powder. Finally, add the cooled ganache and beat until fully combined.

Place the bottom half of the cake into the pan. Spread the whipped cream filling evenly over the surface. Gently place the second half of the cake on top. Cover the cake with the ganache buttercream, spreading smoothly.

Fit a pastry bag with a large star tip and pipe swirls across the surface. Pipe vertical lines from one side to the other to create a tree-bark effect. Dust with powdered sugar and add holly designs using red and green frosting. Serve immediately.