Preheat oven to 350F and line a baking sheet with parchment paper. Add chopped or whole hazelnuts to the baking sheet. Bake for 8-9 minutes for whole hazelnuts and 7-8 minutes for chopped. Cool and then remove any extra skins that come off.
In a large bowl, or stand mixer, cream together butter and powdered sugar until smooth.
Mix in vanilla bean paste, salt, and cinnamon.
Add flour and cornstarch and mix just until the dough comes together.
Add ground hazelnuts and stir until combined.
Add cream or milk 1 teaspoon at a time until dough is cohesive but not sticky.
Scoop 1½ teaspoon portions onto a parchment lined baking sheet.
Refrigerate for 45 minutes.
Preheat oven to 325°F.
Bake for 14–16 minutes until bottoms are lightly golden.
Cool completely before filling.
Spoon about ½ teaspoon (or less) melted chocolate onto the flat side of one cookie and sandwich with another.
Allow chocolate to set before serving or storing.