Toasted Hazelnut Slice 'n' Bake Cookies with Milk Chocolate

INGREDIENTS

3/4 cup

unsalted butter, softened to room temperature

2/3 cup

packed light or dark brown sugar

large egg, at room temperature

1 tsp

pure vanilla extract

2 cups

all-purpose flour (spoon & leveled)

1/2 tsp

ground cinnamon

1/4 tsp

salt

1 cup

toasted and finely chopped Diamond of California hazelnuts, divided1

optional: coarse sugar for rolling

8 oz

milk chocolate, coarsely chopped2