Add the crumbled bacon, chopped spinach, chopped onion or green onion, garlic powder, salt, pepper, and optional red pepper flakes. Stir until everything is evenly distributed.
Divide the mixture evenly among the prepared muffin cups, filling each about 3/4 full. If using, sprinkle a little grated Parmesan over the tops for extra flavor and a light crust.
Bake in the preheated oven for 18–22 minutes, or until the cups are set in the center and lightly golden around the edges. A toothpick inserted in the middle should come out mostly clean.
Remove the muffin tin from the oven and let the cups cool in the pan for about 5–10 minutes. They will puff up in the oven and then settle a bit as they cool—that’s perfectly normal.
Run a small knife around the edges, if needed, and gently lift the cups out. Serve warm, or let them cool completely and refrigerate in an airtight container for up to 4 days.
To reheat, warm in a low oven (300°F/150°C) for 8–10 minutes, or microwave gently in short bursts until heated through.
Variations & Tips
You can nudge these little cups in all sorts of directions depending on what’s in your fridge or what’s coming in from the garden. For a heartier version, add 1/4 cup finely diced cooked ham or breakfast sausage in place of some of the bacon. If you like more vegetables, fold in a few tablespoons of finely chopped bell pepper or mushrooms—just sauté them first to cook out some of the moisture. For a slightly different flavor, swap cheddar for Swiss or pepper jack, or add a teaspoon of Dijon mustard to the egg mixture for a subtle tang. If you’re watching sodium, cut back on the salt and use reduced-sodium bacon or omit it and lean on extra herbs like chives, parsley, or a pinch of dried thyme. These freeze well, too: cool completely, wrap individually, and store in a freezer bag. Reheat straight from frozen in a low oven until warmed through. And if you’re cooking for folks who aren’t low carb, you can tuck a thin slice of bread or a few crushed crackers in the bottom of each cup before pouring in the egg mixture, which gives them a more traditional, quiche-like feel without changing the recipe for everyone else.
