Preheat oven to 350F. Generously grease a 9-inch springform pan with butter line the bottom with a round piece of parchment paper; set aside.
Add the hazelnut meal, cocoa powder, sea salt, cream of tartar, and 1/2 box Bahlsen Waffeletten cookies to a food processor and pulse until the cookies are completely crumbled; set aside.
Melt the chocolate and butter together in a microwave or double boiler. Stir in the pear butter, vanilla extract, and hazelnut extract. Mix in the hazelnut meal mixture.
Use a handheld electric mixer to beat the eggs and brown sugar together in a large bowl until they’re pale golden, light and fluffy, and nearly doubled in volume, about 10 minutes.
Stir 1/3 of the fluffy egg mixture into the chocolate mixture. Once incorporated, fold in another 1/3 of the egg mixture until nearly completely incorporated, and then fold in the remaining 1/3 of the egg mixture. Be careful not to over-mix or deflate the eggs completely; a few streaks of egg in the batter is fine.
Pour the batter into the prepared springform pan. Bake until the cake is set and a wooden pick inserted in the center comes out with just a couple crumbs (do not bake until a wooden pick comes out clean because the cake will be overcooked), about 55 to 60 minutes.
Straight out of the oven, transfer the cake to a wire rack to cool completely to room temperature. Once cooled, cover the cake and transfer it to the fridge to chill for 4 hours or overnight. Once chilled, invert the cake onto a cake platter and peel off the parchment paper.
For the ganache, melt the chocolate and heavy cream together in a microwave or double boiler just until the chocolate is melted (being careful not to overheat), and gently stir to combine. Let the ganache cool a couple minutes, and then starting in the center, spread it across the top of the inverted cake, letting it drip down the sides. Add the toppings decoratively to the top.
Chill the cake until the ganache sets (about 1 hour) before slicing and serving.