Calzone with Spinach and Ricotta

Ingredients

• 2 bags, 284 g (10 oz) each, spinach, trimmed, washed and dried
• 50 ml (¼ cup) olive oil
• 1 small onion, chopped
• 2 cloves, garlic, chopped
• 6 dried tomatoes in oil, chopped
• 1 475 g container, ricotta cheese, drained
• 250 ml (1 cup / 120 g) feta cheese, crumbled
• 2 ml (½ tsp) ground nutmeg
• Salt and freshly ground pepper, to taste
• 600 g (1 lb 5 oz) Pizza Dough, in 4 equal pieces
• 250 ml (1 cup) commercial tomato sauce
• 1 egg yolk, beaten