Step 1

If using fresh fava beans, cook in a small saucepan of boiling salted water until tender, about 4 minutes. Using a slotted spoon, transfer to a colander set in a bowl of ice water (do not cook frozen beans). Drain and peel; transfer to a small bowl.

Step 2

If using fresh peas, return water in saucepan to a boil. Add peas and cook until tender, about 3 minutes (do not cook frozen peas). Drain; transfer to colander in ice water. Drain peas; add to bowl with beans.

Step 3

Heat 2 tablespoons oil in a large saucepan over medium-high heat. Add bacon and tasso and cook, stirring often, until bacon is crisp and fat is rendered, 5-7 minutes. Using a slotted spoon, transfer to bowl with beans and peas; set aside.

Step 4

Add 1 tablespoon oil to drippings in saucepan and heat over medium-high heat. Add reserved shrimp shells and cook, stirring and mashing shells occasionally, until shells are browned and softened, about 4 minutes. Add shallots and garlic and cook, stirring often, until softened, about 2 minutes. Add broth and thyme sprigs. Bring to a boil, reduce heat, and simmer until reduced by half, 15-20 minutes. Add orange and lemon juice, wine, Worcestershire sauce, hot pepper sauce, and sugar. Bring to a boil, reduce heat, and simmer until thickened and reduced by half, 20-25 minutes. Strain mixture through a sieve into a medium saucepan; discard solids. Cover and keep sauce warm.

Step 5

Heat butter and remaining 1 tablespoon oil in a medium skillet over medium-high heat. Season shrimp with salt and pepper. Add shrimp to skillet and cook until golden brown and opaque in the centers, about 1 minute per side. Add reserved meat and vegetable mixture and toss to coat.

Step 6

While sauce is cooking, bring 4 cups water to a boil in a large saucepan. Add 2 teaspoons salt and slowly whisk in grits. Reduce heat to medium-low and cook, stirring often, until thick and creamy, 5-7 minutes. Add mascarpone and butter; stir to combine. Season with salt.

Step 7

Serve grits topped with shrimp mixture and warm sauce.

Step 8

DO AHEAD: Vegetables, bacon, tasso, and sauce can be prepared 2 hours ahead. Let stand at room temperature. Reheat before using.