Place almond flour, stevia/erythritol blend, cocoa powder, baking soda, and sea salt in food processor. Pulse to combine.

Add vanilla extract and butter. Pulse processor until mixture sticks together to form a dough.

Add hazelnuts to the processor. Pulse to chop the nuts and incorporate into the dough. Stop the processor once or twice and break up the dough so that the hazelnuts spread evenly throughout the dough.

Turn dough out onto a piece of parchment. Shape into a log about 2 inches in diameter to about 6-7 inches long. 

Wrap dough in the parchment. Refrigerate at least 2 hours. You can make the dough ahead and refrigerate it overnight if you prefer.

Preheat oven to 375º Fahrenheit. Prepare a baking sheet by lining it with parchment or greasing with coconut oil. I use a silicone coated baking sheet that doesn't require either.

Remove dough from parchment and slice into 16 equal circles. 

Arrange cookies on the prepared baking sheet. Bake for 11-12 minutes or until edges are set. Centers will NOT spring back when lightly touched. Allow cookies to cool on the baking sheet at least 5 minutes, then transfer to a cooling rack so they can cool completely. Be sure they have cooled before drizzling the chocolate overtop.

Place chocolate in a small heavy saucepan. Put saucepan over extra-low heat. (See article above if you don't have a extra-low simmer setting or a heavy saucepan). Heat, stirring chocolate constantly, until completely melted. Remove from heat.

Allow chocolate to cool until it has slightly thickened, but has not set. Using a cake decorating bag or a spoon, drizzle chocolate over the cooled cookies.