Makes 30 cookies
12 oz bittersweet chocolate wafers, divided
8 tbsp unsalted butter
2 large eggs
1 cup sugar
1 tbsp vanilla extract
1 tsp salt
3/4 cup 00 flour
3/4 cup hazelnut flour, plus 1/2 c for rolling
1 tbsp vegetable oil
30 whole hazelnuts, skins removed
In a small saucepan, boil water over medium-high heat. In a heat safe bowl, place over boiling water, being sure the water doesn't touch the bottom of the bowl. Add 8oz chocolate wafers and stir until melted, about 2-3 minutes, Cut butter into 4-5 pieces and add to bowl, mixing to combine, followed by vanilla extract. Remove from heat.
To the bowl, add in sugar and whisk to combine. Add 2 eggs, one at a time and whisk vicariously to combine and incorporate air, resulting in a lighter, fluffier mixture. Whisk for 2-3 minutes. Add in flours and sugar and whisk to combine.
Cover bowl and refrigerate for at least 2 hours, or up to 24 hours.
Remove bowl from the refrigerator, you will need it to sit out for about 15 minutes for the dough to soften a bit in order to be able to scoop it. Preheat oven to 350 degrees. Line 2 large baking sheets for parchment paper and using a small cookie scoop (2 tbsp), portion out 30 cookies. Roll into a ball with your hands and roll into hazelnut flour to coat.
Press your thumb (or a wine cork) into the center or the cookies to create a thumbprint mark. Bake at 350 degrees for 10-12 minutes. Cookies will still look gooey, DO NOT overbake.
In a microwave safe bowl, heat 4 oz chocolate wafers until melted, about 2 minutes. Add in vegetable oil and stir. Fill the center of each cookie and press a hazelnut into chocolate center. Let sit at room temperature for chocolate to firm up.
Store in an airtight container at room temperature for up to 3 days.