Chocolate Brownie Cake with Chocolate Hazelnut Filling and Mocha German Buttercream

INGREDIENTS

Egg

Egg yolks

1 tsp

Vanilla bean paste

1 tsp

Vanilla extract or vanilla bean paste

100 g

All-purpose flour

3/4 tsp

Baking powder

724 g

Bittersweet chocolate

135 g

Brown sugar, dark

100 g

Cocoa powder

24 g

Corn starch

250 g

Dark chocolate, good quality

1 tsp

Kosher salt

1/2 tsp

Salt

625 g

Sugar

125 g

Neutral oil

280 g

Hazelnuts, raw

35 g

Coffee, coarsely ground

6 sticks

unsalted butter, unsalted

125 g

Butter, unsalted

375 g

Whole milk