3 tablespoons extra-virgin olive oil (EVOO)
½ pound meaty bacon, chopped ½-inch dice
2 large shallots, finely chopped
1 round teaspoon sugar
Salt and coarse black pepper
About 2 tablespoons cider vinegar (Rach likes to use Bragg’s)
½ pound white mushrooms, sliced
2 tablespoons fresh thyme, chopped
4 large cloves garlic, finely chopped
2 bunches medium-leaf spinach (¾-1 pound), stemmed, washed and patted dry, chopped
Freshly grated nutmeg, to taste (no more than 1/8 teaspoon)
3 tablespoons Dijon mustard
About ½ cup flat-leaf parsley, finely chopped
12 eggs, beaten
½ pound Gruyere, shredded (about 1½ to 2 cups)
Preheat oven to 375˚F. Heat a 12-inch nonstick skillet over medium to medium-high heat. Add EVOO, 1 turn of the pan, then add bacon and crisp 2-3 minutes. Stir in shallots a minute more, then add sugar, salt and pepper and stir a minute more. Add vinegar and let it absorb, then remove from pan and reserve.
Add remaining oil to pan with bacon drippings, 2 turns of the pan. Add mushrooms and lightly brown, then add thyme, garlic, and salt and pepper. Wilt spinach into pan, then season with salt, pepper and nutmeg.
Whisk Dijon mustard and parsley into eggs. Add bacon mixture back to pan, pour eggs over and gently stir to combine. Settle the eggs and let them set for a minute or so, then transfer to oven and bake about 12 minutes. Top the frittata with Gruyere and bake 12-15 minutes more until puffed and golden. Loosen edges and remove frittata to cutting board or platter, and cool 10 minutes. Cut the frittata into 6 or 9 squares and serve.