Preheat your oven to 400°F (200°C). Pierce each potato several times with a fork. Rub the potatoes with olive oil and sprinkle with a pinch of salt. Place them directly on a baking sheet.

Bake for 60-75 minutes, or until the potatoes are very tender when squeezed and easily pierced with a fork. Remove from the oven and let cool slightly, about 10-15 minutes, until cool enough to handle.

While potatoes are baking, melt 2 tablespoons of butter in a large skillet over medium heat. Add the diced yellow onion and cook until softened, about 3-5 minutes. Add the minced garlic and cook for another minute until fragrant.

Add the chopped shrimp, 2 teaspoons of Old Bay seasoning, and cayenne pepper (if using) to the skillet. Cook for 3-5 minutes, stirring occasionally, until the shrimp are pink and cooked through. Remove from heat and stir in the fresh lemon juice. Set aside.

Carefully slice each cooled potato in half lengthwise. Scoop out the cooked potato flesh into a large mixing bowl, leaving about 1/4 inch of potato attached to the skin to maintain its structure. Keep the potato skins intact.

To the scooped potato flesh, add the sour cream, milk, 4 tablespoons of melted butter, 1/2 cup of shredded cheddar cheese, 1 teaspoon of Old Bay seasoning, garlic powder, smoked paprika, salt, and black pepper. Mash with a potato masher or a fork until mostly smooth, leaving a few small lumps for texture if desired.

Gently fold in about three-quarters of the cooked shrimp mixture into the potato mash. Reserve the remaining shrimp mixture for topping or mixing in later for visual appeal.

Spoon the potato and shrimp filling back into the empty potato skins, mounding it slightly. Place the filled potato halves back on the baking sheet.

Sprinkle the remaining 1/2 cup of shredded cheddar cheese over the top of each potato. You can also add the reserved shrimp pieces on top now, or after baking.

Return the potatoes to the 400°F (200°C) oven and bake for 15-20 minutes, or until the cheese is melted and bubbly and the filling is heated through and lightly golden. If desired, you can broil for the last 1-2 minutes for a darker, crispy cheese topping (watch carefully to prevent burning).

Remove from the oven, garnish with chopped green onions and a lemon wedge if desired. Serve hot and enjoy your delicious shrimp boil twice baked potato!