In a bowl, mix flour, sugar, cocoa, oil, milk, egg and 1 tablespoon Nutella.
Mix all together until you have a smooth mixture. You’ll need to have a soft-ish, creamy texture.
Grab a cup and coat with oil and a mixture of flour and cocoa (just a tiny bit). Shake the excess off.
Pour brownie mixture into the cup (aim to fill no more than 3/4 of the cup).
Add 2 tablespoons of Nutella in the middle. You can add more if you want a richer “lava” in your cake (or use chocolate with a more runny texture when melted).
Place into the microwave on high for 1 min 40 seconds. You may need to experience with that as microwaves have different settings (mine is 850 watts). The secret is to not overcook the batter. The cake should rise a bit, with a fluffy texture and a glossy top.