Coarsely chop the hazelnuts. Reserve some of the half pieces (about 16) to decorate the top of the unbaked scones. Chop the chocolate into a combination of small and large (1/4-inch) pieces. Reserve come of the large pieces to stick into the top of the scones after they are cut, but before brushing them with egg wash.
Add the flour, baking powder, salt, ground cinnamon, and brown sugar to a large bowl and whisk the ingredients together for about 30 seconds. Use your fingers to break up large clumps of brown sugar.
Use a box grater to grate the frozen butter into the dry ingredients. Use your fingers to toss the butter and flour together and combine. Add the chopped hazelnuts and chocolate and toss with the butter and dry ingredients.
Form a well in the middle of the dry ingredients. Add the heavy cream and use a silicone spatula to fold the dry ingredients into the cream. The dough will start to come together and be slightly sticky.
Lightly flour a board or your countertop and turn the dough out onto the surface. Press any remaining bits of flour into the dough by folding the dough over in half and pressing it together. Do this about 4 times.
Form the dough into an 8-inch circle. If you want a perfect circle, use an 8-inch cake pan or plate to get an even circle. Place the cake pan on top of the dough to check the width. Cut the dough into 8 wedges. Press the reserved pieces of chocolate and hazelnut into the top of the scones. Place the scones on a plate and refrigerate for at least 30 minutes and up to 24 hours.
At this point the scones can be frozen. Place them on a sheet tray and freeze. Once frozen, store them in a freezer bag. They will be good in the freezer for 1 month. When ready to bake them, bake them straight from the freezer, no need to thaw them first.