Make the cake: Preheat the oven to 350 degrees F. Lightly oil and flour two 8-inch round cake pans, tapping out any excess flour. Whisk the flour, baking powder and baking soda in a medium bowl; set aside.
Melt the coconut oil and unsweetened chocolate in a small saucepan over medium-low heat, stirring occasionally; remove from the heat. Whisk the hot water and cocoa powder in a large bowl until smooth. Drizzle in the melted chocolate mixture, whisking until combined. Whisk in the granulated sugar and salt until smooth. Whisk in the eggs, one at a time, then add the vanilla. Whisk in the flour mixture just until smooth.
Divide the batter between the prepared pans. Bake until the tops of the cakes spring back when lightly pressed, 30 to 35 minutes. Transfer to a rack and let cool 10 minutes in the pans, then run a knife around the edges and turn out onto the rack to cool completely.
Meanwhile, make the frosting: Beat the butter and salt in a large bowl with a mixer on medium speed until creamy, about 1 minute. Reduce the speed to low and gradually beat in the confectioners' sugar. Increase the speed to medium and beat until combined. Add the vanilla and beat on medium-high speed until fluffy, 2 to 3 minutes. Beat in the milk until smooth.
Assemble the cake: Trim the domed tops of the cakes using a long serrated knife; transfer the scraps to a bowl. Cut each cake into 2 equal layers (leave the layers stacked). Cut both cakes in half, about 1/2 inch off-center. You will have 4 slightly smaller half moons and 4 slightly larger ones.
Stack the 4 larger half-moons, spreading frosting between the layers. Place the stack cut-side down on a piece of parchment paper. Repeat with the smaller half-moons to make another 4-layer stack, then turn the stack cut-side down and attach it to the larger stack using more frosting
Trim the sides of the smaller cake sandwiches to make a slightly pointed shape. Transfer the cake scraps to the bowl.
Trim the curved top of the cake so that it has an even, rounded shape; add the scraps to the bowl. Add 2 to 3 tablespoons frosting to the bowl of cake scraps and mash with a fork until moistened. Pat the scraps mixture around the top, bottom and sides of the cake to round it out and form an egg shape.
Cover the entire cake in a thin layer of frosting (this is the crumb coat; it doesn¿t have to be perfect). Refrigerate until firm, about 30 minutes. Cover the cake with the remaining frosting, building out the egg shape where needed with more frosting. Cover the cake with rows of coarse sugar, nonpareils and candy-coated chocolates. Refrigerate until set, at least 20 minutes.