In a large mixing bowl, whisk the yeast, sugar, and warm water. Set aside for 10 minutes, until it's foamy on top. (If it's not foamy, check your yeast packet, as it might be expired.)
Add the olive oil and stir it into the foamy yeast mixture.
Add the flour, Italian seasoning, and salt, and mix for a minute with a large wooden spoon or silicone spatula until it forms a soft, sticky dough.
Cover the mixing bowl with plastic wrap or a kitchen towel for 30 minutes.
Stretch and Fold 1: Use your hand to scoop a handful of dough from underneath, up one side, up out of the bowl as far as you can stretch it without tearing, then fold it over itself on top. Rotate the bowl 90 degrees and repeat another stretching of the dough up and folding over itself. Repeat rotating the bowl and stretching & folding the dough twice more, until you've completed four stretch-and-folds.Cover the mixing bowl with plastic wrap or a kitchen towel for 30 minutes.
Stretch and Fold 2: Repeat the process for four stretch-and-folds. Cover the mixing bowl with plastic wrap or a kitchen towel for 30 minutes.
Stretch and Fold 3: Repeat the process for four stretch-and-folds. Cover the mixing bowl with plastic wrap or a kitchen towel for 30 minutes.
Stretch and Fold 4: Repeat the process for four stretch-and-folds.
Cover the mixing bowl with plastic wrap or a kitchen towel for 1 hour until it doubles in size and looks bubbly on top.
Shape, Fill, and Proof the Dough
Spread 6 tablespoons of olive oil on the bottom and up the sides of two loaf pans (3 tablespoons in each pan).
Separate roughly one quarter of the dough from your mixing bowl and press it into all the edges of a loaf pan. Repeat with another quarter of the dough in the second loaf pan.
Top with half the marinara sauce (¼ cup on each), half the mozzarella (½ cup on each), and about 8-10 pepperoni slices on each.
Separate the remaining dough in the mixing bowl and gently stretch the dough on top of the toppings in the two loaf pans. Top with the remaining marinara sauce, mozzarella, and pepperoni.
Cover the two loaf pans with plastic wrap and let the dough rise at room temperature for about 2 hours, or until the dough has really puffed up and jiggles when you shake the baking dish.
Add the Toppings and Bake
Preheat the oven to 425°F (230°C).
Coat your fingers in olive oil (don't skip this, or else the dough will stick all over your fingers.) Use your fingers to press dimples into the dough, pressing almost to the bottom of the loaf pan.
Drizzle the remaining four tablespoons evenly over the two loaves.
Bake for 20 minutes, then reduce the oven temperature to 375°F (190°C) and bake for another 20-25 minutes, or until the focaccia is puffed up and golden.
Cool the bread for at least 20 minutes before slicing in the pan. Or you can remove the whole loaf from the pan by first running a knife around the edges and gently using a knife or spatula to release it from the bottom.
Notes
Cheese: Use pre-shredded mozzarella, which has a lot less moisture than fresh mozzarella, so it won’t add too much moisture to the dough. And I find mozzarella has one of the best melting-factors, providing that epic cheese-pull.
Sugar: The tiny bit of sugar won’t make the dough sweet, but I find that it helps jump start fermentation for the yeast.
Equipment: I use two 8.5x4.5 loaf pans, and this recipe works in an 8x4 or 9x5 loaf pan as well, depending on what you have on hand.
Storing: Store your cooled loaves wrapped in plastic wrap in the fridge for a few days. I usually reheat slices in the microwave or toaster oven.