Make the cake: Preheat the oven to 350 degrees F. Butter two 9-inch round cake pans and line the bottoms with parchment paper, then butter the parchment. Dust the pans with flour and tap out any excess.
Whisk the flour, malted milk powder, cocoa powder, baking powder, baking soda and salt in a large bowl. Beat the butter and sugar in a separate large bowl with a mixer on medium-high speed until light and fluffy, about 6 minutes. Beat in the eggs, one at a time, then beat in the vanilla. Reduce the mixer speed to low; beat in the flour mixture in three batches, alternating with the buttermilk. Beat until smooth, about 1 more minute.
Divide the batter between the prepared pans; tap on the counter to remove any air bubbles. Bake until a toothpick inserted into the centers of the cakes comes out clean, 30 to 35 minutes. Transfer to a rack; run a knife around the edges of the cakes and let cool 10 minutes, then turn out the cakes onto the rack to cool completely. Discard the parchment.
Meanwhile, make the frosting: Whisk the milk, malted milk powder, flour, cocoa powder and salt in a small saucepan until combined. Bring to a boil over medium-high heat, whisking, until the mixture is thick like pudding, 1 to 2 minutes. Transfer to a bowl and press plastic wrap directly onto the surface. Refrigerate until completely cool, about 11/2 hours.
When you¿re ready to assemble the cake, finish the frosting: Remove the malted mixture from the refrigerator and whisk until creamy. Beat the butter and sugar in a large bowl with a mixer on medium-high speed until fluffy, about 8 minutes. Add large spoonfuls of the malted mixture, beating 1 to 2 minutes after each addition and scraping down the bowl as needed (the frosting will look separated). Continue beating until the frosting comes together and is light and fluffy, about 3 more minutes. (Do not chill!)
Assemble the cake: Place 1 cake layer on a platter. Spread with 1 heaping cup of the frosting. Top with the second cake layer. Cover the top and side with more frosting, then build up a ring around the top of the cake with the remaining frosting to create a nest. Refrigerate the cake until the frosting firms up, about 30 minutes.
Meanwhile, make the topping: Toss the shredded wheat in a large bowl with the melted butter, then add the sugar and toss again. Spread in a single layer on a baking sheet and bake at 350 degrees F until lightly browned, about 15 minutes. Melt the chocolate in a large microwave-safe bowl in 20-second intervals, stirring, until smooth, 1 to 2 minutes. Let cool slightly, then stir in the shredded wheat mixture until completely coated. Press the topping all over the top and side of the cake. Refrigerate until set, at least 30 minutes or overnight. Fill the nest with candy eggs.