In a medium sauce pan, pour the honey, add the light brown sugar, butter pieces, and salt.
Cook over medium heat, stirring occasionally until the butter has melted and the sugar has dissolved.
Line an 8-inch round pan with parchment paper, pour the syrup into the pan then evenly spread the hazelnuts over. Set aside.
Preheat oven to 335F
Using a food processor, process the hazelnuts and potato starch until finely ground.
Move the ground hazelnuts into a medium bowl, then mix in the flour, baking powder, baking soda, nutmeg, and orange zest, set aside
In a bowl of a standing mixer, fitted with the paddle attachment, beat the butter, sugar, and honey on medium speed for 4-5 minutes or until light and fluffy.
Increase speed to medium-high and add the vanilla extract followed by the eggs, one at a time waiting for the first egg to fully incorporate before adding the second. Scrape the sides and bottom of the bowl.
Reduce speed to low, and add the hazelnuts-flour mixture in three additions altering with the sour cream starting and end ending with the dry mixture. Add the last portion of the flour mixture using a rubber spatula.
Scoop the cake batter into the prepared pan over the syrup and hazelnuts, then use an offset spatula to evenly spread it.
Bake for 35-40 minutes or until a toothpick comes out clean at the center of the cake.
Remove, allow to cool for 2-3 minutes then invert the cake onto your serving plate, or an 8-inch cake board.
Make sure all of the ingredients are at room temperature.
If you do not have a stand mixer, you can use a hand mixer.
The cake is also great when baked “naked” meaning without the syrup or extra hazelnuts. You may need to reduce the baking time to 25 minutes.
If you do not have potato starch do not replace it with cornstarch. Increase the amount of flour to 3/4 cup instead