Lightly spray a 9 inch spring form pan with pan spray.
Line the bottom of the inside of the pan with a 9 inch round piece of parchment paper or aluminum foil.
Wrap a piece of aluminum foil around the outside base of the pan so that the foil comes up the sides of the pan about one inch.
Place the prepared pan in a large roasting pan or baking pan that is at least one inch deep.
Set the pan aside.
Place the hazelnuts, oatmeal, and brown sugar in the bowl of a food processor.
Pulse the processor a few times then turn it on.
Grind until the nuts are fine but not oil.
Add the melted butter and mix just to combine all of the ingredients in the processor bowl.
Press the crust mixture evenly into the bottom of the pan.
Break or cut the Moonstruck dark chocolate into small pieces and place into the top of a double boiler along with the 1 1/4 cup butter.
Fill the bottom of the double boiler with about one inch of water.
Bring to a boil then remove from the heat.
Place the top of the double boiler over the steaming water.
Stir until the chocolate and butter mixture have melted.
Add the hazelnut butter, brewed espresso beverage, and the Grand Marnier.
Stir to thoroughly combine.
Whisk the eggs and the 3/4 cup of brown sugar until foamy.
Add the chocolate mixture and stir to thoroughly combine.
Pour the batter into the prepared spring form pan with the crust in the bottom.
Place the roasting or baking pan holding the filled spring form pan on the middle rack of the oven.
Add about one inch of boiling water to the roasting or baking pan.
Carefully slide the rack into the oven.
Bake for approximately 45 minutes until the filling has set but the center is still shiny.
Remove the spring form pan from the oven and place on a cooling rack.
Cool completely in the spring form pan.
Place the cooled cake into the refrigerator and chill for at least six hours. Overnight is better.
Chop the chocolate and place in a stainless steel or glass bowl.
Place one inch of water in a small heavy saucepan.
Place the saucepan on the stove and bring the water to a simmer.
Remove the saucepan from the stove.
Place the bowl containing the chopped chocolate on top of the pan of simmering water.
Stir the chocolate until it is completely melted.
Remove the bowl from the top of the pan and dump the water out.
Place the cream and light corn syrup into the sauce pan and bring to a boil.
Pour the hot liquid over the melted chocolate.
Whisk the hot liquid and the chocolate together to completely combine.
Set the chocolate mixture aside and allow the Ganache to cool for five minutes.
Whisk the softened butter into the chocolate mixture.
Finish and serve:
Remove the sides of the spring form pan.
Place a piece of plastic wrap or foil over the top of the cake.
Invert the cake onto a flat dish.
Peel the paper or foil off of the bottom crust.
Invert the cake onto a 9 inch cardboard cake round.
Place the cake on a cooling rack over a cookie sheet.
Pour the Ganache over the cake, using a small icing spatula to coax the Ganache over the sides of the cake. If necessary, use the spatula to spread the Ganache on the sides of the cake. The cake should be completely covered with Ganache.
Allow the Ganache to set up until it is firm.
If you are not serving right away, return to the refrigerator.
Cut into servings using a knife dipped in hot water and wiped dry each time you make a slice.
Place on a serving plate and garnish with whipped cream and fresh berries.