Snip the end of a piping bag and insert the piping tip. Add Nutella to the bag and set it aside.
In a small bowl, mix sugar with instant espresso powder and set aside.
Add oil to the skillet until the level reaches about 1.5 to 2 inches deep. Heat on medium. Oil is ready when tiny bubbles form around the biscuit dough when it touches the surface of the oil.
Use a bottle cap or apple corer to cut holes into the center of each biscuit.
Add 3-4 biscuits to the skillet at a time. Fry for about 3 minutes until the sides turn a light golden brown. Flip, and then fry for an additional 3 minutes.
Remove from oil and place donuts on a cooling rack.
While still hot, carefully dip each donut into the bowl of espresso sugar, coating both sides.
Allow donuts to cool slightly, then insert the piping bag with Nutella into each donut and fill with about 2-3 tablespoons of the desired amount.