In a small mixing bowl, whisk together yeast, warm water, sugar and olive oil. Let sit for about 3 minutes to fully dissolve and activate the yeast.
In a large mixing bowl, whisk together flour and salt.
With a rubber spatula, gradually mix the yeast mixture into the flour until just combined and dough barely holds together. Turn the dough out onto a clean counter surface dusted with flour.
Knead the dough with flour-dusted hands until the dough has become smooth and elastic, about 10 minutes. The surface should be tight and silky and bounce back slightly when pressed. Lightly grease a large mixing bowl with olive oil and place the dough in it.
Cover the bowl tightly with plastic wrap and set in a warm place to rise until doubled in size, 1 to 2 hours.
Once doubled, punch the dough down and divide it into 2 equal pieces. Knead each 1 slightly to form a uniform ball. Set aside and cover them with a kitchen towel or plastic wrap to rest for 30 minutes.
Cook's Note: Dough can be made the day before and refrigerated overnight once it is divided. Keep covered tightly in plastic wrap or in a sealed food storage bag.
Yield: 2 dough balls
Preheat oven to 450 degrees F.
Lightly dust the work surface and rolling pin with flour. Roll the dough out into an 8 by 11-inch oval.
In a medium bowl, mix the spinach, ricotta, and mozzarella and season with salt and pepper, to taste.
Place all the filling on 1 half of the dough leaving a 3/4-inch border along the edge.
Fold the remaining dough over the filling until the edges line up and pinch the edges together to seal. Gently roll the pinched edges under to form a decorative rim.
Place the calzone on a baking sheet dusted with cornmeal and brush the top with olive oil.
Bake until golden brown and the center is hot and melted, 25 minutes, rotating midway through cooking.