Preheat oven to 170 C / Gas 3. Put 10 cake cases into a 12 hole cake / Yorkshire pudding tin.
Put Nutella® in a mixing bowl with the egg and mix until smooth. Stir the flour in till combined. Add milk if needed - I find it sometimes needs it, sometimes not.
Put 2 teaspoons of mix into each cake case. I find it sometimes makes 9, sometimes 10.
Place into the oven for about 12 to 15 minutes. They will rise a bit but are supposed to be quite dense if made with plain flour. Check at 12 minutes with a cocktail stick. If it comes out with gooey crumbs then take them out.
Place on wire rack to cool. Best eaten slightly warm but can be eaten cold too.
You can sprinkle chopped nuts on these before baking or mix into mixture if you prefer. Or add any ingredient that may go with a brownie such as chocolate chunks or glacé cherries.