Remove the shells from the shrimp and devein if necessary.
Butterfly the shrimp by slicing a lengthwise incision along the curve of the shrimp, making sure not to slice all the way through.
Place the butterflied shrimp in a large bowl.
Add the olive oil, white wine, lemon juice, garlic, salt, pepper, and crushed red pepper flakes to the bowl, stir to combine.
Set the bowl aside to marinate while you make the stuffing.
Place softened butter, focaccia, garlic, shallot, parsley, Parmesan, lemon zest, egg, salt, and pepper.
Using a fork, stir and mash the stuffing together until combined.
Arrange the shrimp in the prepared casserole dish, cut side down, and fanned out. Reserve any marinade remaining in the bowl.
Using a small scoop or tablespoon measure, portion the stuffing, and place it on top of the shrimp. Secure the stuffing in place using the tails of the shrimp. Drizzle with the remaining marinade.
Place the casserole dish in the oven and bake for 15 to 20 minutes or until the shrimp have turned pink and the butter is bubbly.
Increase the oven temperature to broil on low and continue to bake for 3 to 5 minutes or until the stuffing is golden brown.