Pre-heat the oven to 350 degrees F. Lightly grease an 8x8” or round baking dish.
Combine almond flour, baking powder and salt in a mixing bowl. Add cold butter to the bowl and incorporate the butter into the flour using a pastry cutter or fork. Combine until the mixture is in gravel-sized pieces.
Lightly whisk the egg white in a separate bowl, then add it to the flour mixture. Stir until combined. It will still be a bit lumpy.
Using your hands or a spoon, spread the mixture in the bottom of the baking dish.
To prepare the gravy, brown the ground sausage in a large skillet over medium-high heat, breaking into small pieces as it browns. When the meat is cooked through, sprinkle half of it over the crust in the baking dish. To the remaining sausage, add the butter and almond flour and whisk it together. Let it cook for 2 minutes.
Add the heavy cream and water and whisk constantly until well combined. Turn the heat down to medium low and cook for 3-5 minutes, until thickened. Season with salt and pepper, to taste.
While the gravy is cooking, whisk the eggs (2 eggs plus the leftover yolk from the egg used in the filling), plus a sprinkle of salt and pepper. Pour the eggs over the sausage in the baking dish. Top with cheddar cheese. Pour on ¾ of the gravy. Bake for 30 minutes, or until the center of the casserole is firm.
Use the remaining gravy to pour over each individual serving.