Stack the tortillas, roll them up tightly, and cut into 6 equal pieces. Stand each piece upright in a heavy-duty cupcake case. If using regular paper cases, place them inside a muffin tin so they hold their shape.
Tuck the chorizo slices between the layers of each rolled tortilla, keeping the spiral shape. Place half a cherry tomato in the centre.
Whisk together the eggs, milk, chives, salt and pepper. Pour the mixture evenly over the tortilla cups, allowing it to soak into the layers.
Bake for about 20 minutes, or until the custard is set. Sprinkle with mozzarella and bake for another 5 minutes, until the tops are melted and golden.
Garnish with extra chives and serve warm. If serving at a party, keep them in the cupcake cases as they look much more attractive this way.