In a large mixing bowl, whisk together 2 ½ cups flour, 1 tbsp baking powder, 2 tbsp granulated sugar, 1 tsp salt, 1 tsp cinnamon & ½ tsp nutmeg until combined.
Using a cheese grater, grate 10 tbsp cold butter directly into the dry mixture. Use your hands or a pastry cutter to gently toss and rub the butter into the flour until it forms a mealy, crumbly texture with pea-sized pieces of butter throughout.
In a separate small bowl, whisk together 1 egg and 1 cup eggnog until smooth. Pour the egg–eggnog mixture into the dry ingredients. Stir just until the dough comes together. Sprinkle your work surface with flour and use your hands to mold the dough it into a large rectangle, flattening out with a rolling pin until about 1" thick.
In a small separate bowl, combine the 4 tbsp softened butter, ½ cup brown sugar and 1 tbsp cinnamon to make your cinnamon roll filling. Spread it out evenly onto your scone dough.
Begin rolling the dough lengthwise tightly just like a traditional cinnamon roll. Use a sharp knife to slice into 6–8 pieces (either squares or triangles). Arrange the pieces tightly together on a lined baking sheet and brush the tops with heavy cream to keep moist while baking.
Bake at 350°F for 22- 30 minutes, or until lightly golden and baked through. Some butter may escape from the sides while baking, that's okay!
Combine 4 tbsp powdered sugar with 1-2 tbsp eggnog depending on desired consistency. Glaze warm and enjoy!