Place a 3-quart pot over medium-high heat. Add the milk and cream. Slowly whisk in the cornmeal. When the grits begin to bubble, turn the heat down to medium low and simmer, stirring frequently with a wooden spoon. Allow to cook for 10 to 15 minutes, until the mixture is smooth and thick. Remove from heat and stir in the butter, thin it out with a little extra cream. Season with salt and pepper.
For the shrimp:
Place a deep skillet over medium heat and coat with the olive oil. Add the onion and garlic; saute for 2 minutes to soften. Add the sausage and cook, stirring, until there is a fair amount of fat in the pan and the sausage is brown. Sprinkle in the flour and stir with a wooden spoon to create a roux. Slowly pour in the chicken stock and continue to stir to avoid lumps. Toss in the bay leaves. When the liquid comes to a simmer, add the shrimp. Poach the shrimp in the stock for 2 to 3 minutes, until they are firm and pink and the gravy is smooth and thick. Add the cayenne pepper, Tabasco and lemon juice. Season with salt and pepper; stir in the parsley and green onion. Spoon the grits into a serving bowl. Add the shrimp mixture and mix well. Serve immediately.