TO MAKE MORNAY SAUCE: Melt butter in a medium saucepan. Add flour and stir for one minute. Add in 2 cups milk. Cook until thickened.
Whisk in 3/4 cream to thin sauce and add 1/3 cup grated Parmesan cheese. Season with salt and pepper.
TO MAKE GNOCCHI: In medium saucepan melt 1/3 cup butter in 1 cup plus 2 tablespoons milk. When butter has melted, season with salt and pepper. Remove saucepan from heat and add in 1 cup all purpose flour all at once. Whisk until smooth.
Return saucepan to heat and, with a wooden spoon, cook until the mixture sizzles and comes away from the sides of the pan. (This is called a panade). Transfer to a large bowl and immediately cover surface with plastic wrap so that a skin does not form. Cool to room temperature.
When mixture has cooled, add the eggs, one at a time. Do not add the next egg until the first is entirely absorbed. When the eggs have been fully incorporated add 3 1/2 ounces grated Gruyere cheese.
BOILED VERSION: Bring water to a boil. Fill a pastry bag, fitted with a 3/4 inch tip with gnocchi mixture. Rest metal tip of pastry bag on edge of pan and press the dough out. As 1/2 inch of gnocchi dough emerges, cut with a knife or scissors and let the dough fall into the water.
Do in batches of 20 or 30. Cook for 4-5 minutes, then remove gnocchi to a cloth towel with a slotted spoon (gnocchi will deflate as they cool). Serve sauce over cooked gnocchi.
BAKED VERSION: Preheat oven to 375 degrees. Put some Mornay on bottom of a shallow 9x13 casserole dish. Fill a pastry bag, fitted with a 3/4 inch tip with gnocchi mixture. As 1/2 inch of gnocchi dough emerges, cut with a knife or scissors. Arrange gnocchi in one or, at most, two layers.
Spread remaining sauce over top, spreading it evenly. Sprinkle top with 1/4 cup grated Gruyere. Bake for 45 minutes or until gnocchi have swollen up again and absorbed sauce. Serve immediately before gnocchi deflate.