Preheat oven to 350 degrees. Line a cupcake tin with paper liners. Set aside.
In the bowl of a stand mixer, add sugar, flour, cocoa powder, baking soda, baking powder, and salt. Fit the stand mixer with whisk attachment and lower. Mix on low until dry ingredients are completely combined.
Add eggs, buttermilk, coffee, oil, and vanilla. Mix until completely combined, about 2 minutes. The mixture will be runny. Scoop into prepared muffin tin, filling each cup 2/3 full. If you fill any higher, the cupcakes will overflow while baking.
Bake in preheat oven for 17 minutes or until toothpick comes out COMPLETELY clean, without any crumbs. Remove from oven and let them cool on a wire rack. Let cupcakes cool completely before topping them.
Place Nutella in microwave safe bowl and microwave 15 seconds to thin it out a little bit. Stir with a spoon. Place crispy chocolate crumbles into a separate medium bowl. Dunk the top of a cooled cupcake into the Nutella and then into the crumbles. Repeat with remaining cupcakes.
Serve immediately or store for up to 2 days.