Preheat oven to 300°F. Prepare three 8-inch cake pans with parchment paper and grease the sides.

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

Add eggs, milk, vegetable oil, and vanilla to the dry ingredients and mix until smooth.

Stir in water until the batter is thin and smooth.

Divide batter evenly among the pans and bake for 30-33 minutes. Cool completely.

Beat butter and Nutella until creamy. Gradually add powdered sugar and heavy cream, beating until smooth.

Level the cakes, layer with buttercream, and frost the outside.

Make ganache by heating Nutella, chocolate chips, and heavy cream until melted and smooth.

Drizzle ganache on the cake, then pipe remaining frosting around top edge. Decorate with Ferrero Rocher candies.

Serve once ganache has set. Store leftovers in an airtight container.