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1
Preheat the oven to 425u00b0F.
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2
To make the crust:
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3
In a medium bowl, stir together the flour, baking powder, and salt. Make a well in the center of the mixture.
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4
In a measuring cup, whisk together the milk, olive oil, and melted butter. Slowly pour the milk mixture into the well, stirring until just blended and the mixture comes together into a rough mass.
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5
Turn out the dough onto a lightly floured work surface and roll out into a 10-by-13-inch rectangle.
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6
Transfer the dough to a baking sheet/tray. Pierce the dough all over with a fork.
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7
To make the topping:
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8
In a large skillet over medium heat, melt the butter with the olive oil. Add the onions and cook, stirring frequently, until softened and lightly browned, about 10 minutes.
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9
Add the thyme, sugar, and salt and pepper to taste, reduce the heat to low, and cook, stirring frequently, until the onions are soft and caramelized, about 20 minutes.
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10
Spread the onion mixture evenly over the dough.
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11
Sprinkle with the cheeses, cut into squares with a pizza wheel or a sharp knife, and bake until the crust is golden and the cheese is bubbling, about 20 minutes.
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12
Transfer to a wire rack and let cool a bit on the pan. Serve warm or at room temperature.
