Preheat your oven to 350°F (175°C) and grease two 9x2.5 inch cake pans.

In a mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt until evenly combined.

In a separate bowl, beat together the eggs, mayonnaise, and vanilla extract until smooth.

Carefully add the dry mixture to the wet ingredients, stirring gently until just combined.

Fold in the melted chocolate until evenly distributed.

Divide the batter between the prepared pans and bake for 30-35 minutes, until a toothpick comes out with a few moist crumbs.

Let the cakes cool in the pans for about 10 minutes, then transfer to wire racks to cool completely.

For the frosting, melt chocolate and mix with unsalted butter until smooth, then gradually add confectioners' sugar.

Once the cakes are cool, frost the top of one layer, stack the second layer on top, and frost the top and sides.