Remove the heads and tails from the shrimp, and reserve for shrimp broth. Devein the shrimp and refrigerate while making shrimp broth.
Make the shrimp broth: Rinse the shrimp shells with cool water. Heat a 4-quart pot over medium-high heat. Add the shrimp shells and cook until pink. Cover with the water and bring to a boil. Reduce the heat to a simmer and continue to cook, uncovered, until the liquid has reduced to 1 quart, 45 minutes to 1 hour. Strain the stock and cool over an ice bath.
Add the salt and bay leaves to the cooled stock, whisking until the salt is dissolved. Set the grits in a 4-quart pot and top with the shrimp. Cover the grits and shrimp with the brine and stash in the fridge for at least 6 hours or up to overnight.
After the 6-hour brine, remove any chaffs or hulls from the grits that may be floating on the surface. Remove the shrimp from the brine.
Bring the grits to a simmer over medium-high heat, whisking continuously until the grits boil to avoid lumps. Reduce the heat and cook the grits until tender and creamy, 30 to 35 minutes. Add a tablespoon of butter and stir to combine. Cover to keep warm while cooking the shrimp.
Toss the shrimp with the lemon juice, hot sauce, and Old Bay. Set aside.
Cook the bacon until crisp in a large cast-iron skillet over medium-high heat. Remove from the pan to paper towels to drain. Add the shrimp and cook until pink, about 2 minutes per side. Coarsely chop the bacon and return to the pan and add the green onion. Stir to combine.
To serve, ladle grits into a bowl and scatter the shrimp and bacon mixture over the top. Drizzle with any remaining bacon grease.