In a medium pot, bring the broth to a simmer and keep hot over low heat.

In a medium, heavy saucepan, melt oil and 2 tablespoons of butter over medium heat. Add the leeks and saute until tender but not brown, 5-6 minutes. Add the rice and stir to coat with the butter. Add the wine and simmer, stirring, until the wine has evaporated, about 3 minutes. Add a ladle-full (about 1/2 cup) of the hot broth and stir until almost completely absorbed, about 2 minutes. Continue cooking the rice, adding the broth 1/2 cup at a time, stirring constantly and allowing each addition of the broth to absorb before adding the next, until the rice is tender but still firm to the bite and the mixture is creamy, 15-20 minutes. Remove from the heat. Stir in the remaining tablespoon of butter, Parmesan, mascarpone cheese, the lemon zest and juice, and season with salt and pepper to taste. If rice thickens while you prepare the scallops, add a bit more hot broth or water just before serving.

Add butter to a small saucepan set over medium heat. Cook, stirring or swirling the pan every few seconds, until the foam subsides and the butter begins to turn golden brown and smells nutty, about 3 minutes. Stir in garlic and let it sizzle for about 10-15 seconds then add and lemon juice and salt and pepper, to taste; set aside.

Place scallops on a layer of paper towels and season with salt on all sides. Top with more towels and thoroughly pat dry. Let rest in the refrigerator for 15 minutes. Cook the risotto while you wait.

Remove salted scallops from the refrigerator and pat dry again. Season lightly with a little more salt. Heat vegetable oil in a large stainless steel or cast iron skillet over high heat until lightly smoking. Add scallops, leaving space between each one to prevent excess steaming. Press each scallop down very lightly with a spatula to ensure good contact with the pan.

Cook scallops without moving them until well browned on first side, about 1-2 minutes. Carefully flip scallops and cook until scallop is just cooked through, about 1 minute longer. Transfer scallops to a paper towel–lined plate to drain. Serve immediately on top of risotto, and drizzle with a tablespoon or two of brown butter sauce and a few peppers, if desired.