Put the flour in a large bowl and stir in the yeast, 1 tsp olive oil and 100ml warm water. Mix together until you have a soft smooth dough. Tip the dough out on to a lightly floured work surface and knead for 10-15 minutes until it's soft and stretchy.
Wash the spinach and place in a large saucepan with just the water that clings to its leaves. Heat gently until it wilts, then tip into a colander and leave to cool. When cool enough to handle, squeeze out the excess liquid. Heat the remaining oil and gently cook the garlic for just a few seconds, then add the spinach and stir for 1 minute.
Lightly dust the work surface with flour, then roll out the dough to 3mm thick and cut out 4 x 10cm rounds. Spoon the spinach on one side of each circle. Make a well in the spinach, then crack an egg on top of each round. Sprinkle over the mozzarella, then fold over the dough and crimp to seal. Brush with milk and leave to rise in a warm place, covered with oiled clingfilm, for up to 40 minutes.
Meanwhile, preheat the oven to 220°C/fan 200°C/gas mark 7. Bake the calzones for 12-15 minutes until the pastry is puffed up and golden.