Popular British chef Jamie Oliver joins Martha in the kitchen to prepare a mouthwatering calzone with mushroom filling.
Heat the oven to 500 degrees, with a pizza stone placed on lowest shelf position, for at least 30 minutes.
Heat olive oil in a large skillet over medium-high heat. Add mushrooms and stir to coat. Add garlic and thyme; cook until mushrooms are softened and fragrant. Add butter and stir until melted and mushrooms are coated; season with salt and pepper.
Add tomato sauce and stir to combine. Working in batches, add spinach and cook until wilted. Continue cooking until mixture is thickened and most of the liquid has been absorbed, about 3 minutes.
Sprinkle 2 baking sheets with flour and set aside. Divide dough evenly into 4 pieces. On a lightly floured work surface, roll out each piece of dough into a 1/8-inch-thick circle, about 12 inches in diameter. Set aside.
Divide spinach and mushroom mixture evenly between rolled out pieces of dough. Top each with one-quarter of the mozzarella and season with salt and pepper. Fold dough in half over filling and crimp as desired to seal. Place on prepared baking sheet to transfer to oven, then transfer to pizza stone. Cook until dough is puffed up and golden and filling is hot, 10 to 15 minutes. Serve immediately.