Preheat oven to 350°; place rack in center of oven. Freeze sugar cookie dough 1 hour. Remove from freezer, and place on cutting board. Cut dough into 1/4-inch slices (about 28–32 slices); arrange 2 inches apart on 2 parchment paper–lined baking sheets. Combine brown sugar, chopped pecans, cinnamon, and, if desired, nutmeg in a small mixing bowl. Top cookies with 3/4 teaspoon streusel. Bake 12 minutes or until edges are crisp and browned. Let cool on baking sheet 3 minutes; remove to a wire rack to cool completely.