Special equipment: a 1-quart (6-inch ramekin)
Put the pizza dough in a medium bowl and coat well with 1 tablespoon of the oil. Cover with plastic wrap and put in a warm place until doubled in bulk, about 1 hour depending on the dough.
Meanwhile, preheat the oven to 400 degrees F. Put the garlic, bell peppers and onions in a food processor and pulse until finely chopped, scraping down the sides of the bowl halfway through.
Heat the remaining 1 tablespoon oil in a medium saucepan over medium-high heat until shimmering. Add the sausage and cook, breaking it up with a wooden spoon, until lightly browned, about 4 minutes. Add the onion mixture and cook, stirring occasionally, until the moisture has evaporated from the pan and the onions are soft, about 5 minutes. Stir in the marinara sauce, oregano, red pepper flakes, 1/4 cup water, 1/2 teaspoon salt and several grinds of black pepper. Bring to a simmer, reduce the heat to medium low and cook, uncovered, stirring often, until thick, about 15 minutes.
Brush the sides and lip of a 1-quart (6-inch) ramekin with the butter. Line the bottom and sides with the Havarti. Fill with 1 1/2 cups of the hot marinara-sausage sauce. Reserve the remaining sauce for another use. Gently pull and stretch the pizza dough into a 10-inch circle and place it over the ramekin, leaving a 2-inch overhang all around. Gently press around the edges of the ramekin to lightly seal. Put on a baking sheet and bake until golden brown and the top sounds hollow when you tap it, about 30 minutes.
Carefully remove the baking sheet from the oven, transfer the ramekin to a heatproof surface and place a plate on top. Carefully invert the ramekin onto the plate, using a spoon to gently pry the dough from the dish. Serve hot.
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