-
1
Put oven rack in middle position and preheat oven to 350u00b0F. Lightly oil a 15- by 10-inch shallow baking pan, then line bottom and all 4 sides with parchment paper, allowing 2 inches of parchment to hang over short sides of pan, and lightly brush parchment (except overhang) with oil.
-
2
Heat 1 teaspoon oil in a 12-inch heavy nonstick skillet over moderately high heat until hot but not smoking, then cook sausage, stirring, until finely crumbled and cooked through, about 2 minutes. Transfer to a bowl and keep warm, covered.
-
3
Add remaining 2 teaspoons oil to skillet and saute garlic and scallions, stirring, until golden, about 3 minutes. Add mushrooms, pepper, and 1/4 teaspoon salt and saute, stirring, until mushrooms are softened and golden, about 8 minutes. Add sausage and spinach to skillet and saute, stirring, 3 minutes. Transfer half of spinach mixture to a food processor and add water, then blend until finely chopped. Return to skillet, stirring to combine, and keep warm, covered.
-
4
Blend whole eggs, whites, milk, Parmigiano-Reggiano, and remaining 1/2 teaspoon salt in a blender until smooth and frothy.
-
5
Pour egg mixture into baking pan and bake until firm, about 10 minutes. Remove from oven and leave oven on.
-
6
Sprinkle egg layer evenly with half of Gruyere, then spoon spinach filling evenly on top and sprinkle with remaining Gruyere. Bake just until cheese melts, about 5 minutes.
-
7
Position pan on a work surface with a long side nearest you, then gently roll up egg layer toward you, using parchment as an aid and holding filling in place with your fingers.
-
8
Cool roll in pan on rack 10 minutes, then transfer to a platter using 2 large spatulas. Trim ends and gently cut into 8 slices with a serrated knife.
