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1
Heat 2 tablespoons oil in a large pan over med-high heat.
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2
Add in onions and season with salt and pepper.
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3
Cover the onions with a piece of foil and cook, stirring occasionally, until they start to soften, 2-3 minutes.
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4
Remove the foil and continue cooking until fully softened, about 5-6 minutes.
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5
Add in the tomato paste; cook/stir occasionally, until it smells sweet and has caramelized, 2-3 minutes.
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6
Add in the wine and scrape the pan with a wooden spoon to loosen any browned bits that may be stuck to the bottom.
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7
Cook until the wine has almost completely evaporated, 1 minute; turn off the heat and reserve.
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8
While the onions cook, place a big skillet over med-high heat with the remaining tablespoon of oil.
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9
In a big mixing bowl, use your hands to combine the ground sirloin, pepperoni, parsley, oregano, and red pepper flakes.
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10
Season the meat with salt and pepper, then score the meat into 4 parts using the side of your hand.
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11
Form 4 large patties thinner in the center than at the edges for even cooking and to prevent the burgers from bulging.
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12
Cook for 4-5 minutes per side for medium doneness.
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13
Preheat the broiler.
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14
While the burgers are cooking, heat the butter and garlic together in a small pot over medium heat.
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15
When the butter melts, remove the pot from the heat to infuse the butter with the garlic flavor.
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16
While the butter is melting, place the bread slices on a baking sheet and toast them under the broiler until golden brown on each side.
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17
Brush the toasts with the garlic butter and sprinkle with the grated cheese.
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18
Place the toasts back on the baking sheet and top each with one burger.
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19
Divide the onion mixture among the four burgers and top each one with two slices of cheese.
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20
Slide the burgers under the broiler to melt the cheese, 2-3 minutes.
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21
Serve the burgers with a knife and fork, and with your favorite salad on the side.
