Pre heat the oven at 350 F. Grease a 9-inch pan lined with parchment paper.
Using an electric mixer on medium high speed, beat together the butter with sugar, until it looks fluffy and mix looks slightly changed in color. It will take 2-3 minutes. Lightly add one egg at a time, and until each one gets incorporated.
The batter might look curdled or separated. Don’t worry it will come together. Add in the hazelnut flour, all-purpose flour along with baking powder and salt. Mix everything on low speed until it comes together. Stir in chopped hazelnuts and if using, frangelico as well.
Transfer the batter in the prepared pan and smooth out the top. Bake for 40-45 minutes or until a toothpick or knife comes out clean and the cake looks done. The cake might look darker than other cakes.
Remove it from the oven, let it cool in the pan for 10 minutes. Take it out on a cooling rack and let it cool completely.
While the cake is cooling, make ganache.
In a microwave or stove top, heat up the heavy cream just enough that the chocolate can melt.
Add the chocolate chips and whisk it well until it melts, and the ganache looks shiny and smooth and there are no lumps in the it.
Once the cake is completely cool, drizzle ganache on the cake right in the middle (check pics) and going sideways to ensure that the sides are also covered in chocolate ganache. Make sure to put a tray underneath your cake while you pour the ganache to catch all the extra drippings.