Prepare the dough by combining flour, yeast, salt, and olive oil in a large mixing bowl. Gradually add warm water until a shaggy dough forms. Knead for 8-10 minutes until smooth, then let rise until doubled in size, about 2 to 2½ hours.

While the dough rises, prepare the filling by mixing ricotta cheese, chopped spinach, salt, and pepper until well combined.

Once the dough has risen, punch it down, divide it into two equal portions, and roll each into a 10-11 inch circle.

Assemble the calzones by placing filling on one half of the dough circle, fold over, and crimp the edges.

Preheat the oven to 450°F (232°C). Place calzones on a parchment-lined baking sheet, make slits on top, and let rest for 30 minutes.

Bake the calzones for 18-22 minutes, until golden brown, then cool slightly on a wire rack before serving.