Preheat oven to 350°F (175°C).

Dice the bacon and cook in a skillet over medium-high heat until crisp.

Transfer bacon to a paper towel-lined plate to drain.

Discard all but 1 tablespoon of bacon drippings from the pan.

Add chopped yellow onion and shallot to the pan.

Sauté for 5 minutes or until tender.

Stir in finely chopped parsley.

In a mixing bowl, whisk together the eggs, half-and-half, dry mustard, ground nutmeg, salt, and pepper.

Add the onion mixture and bacon to the egg mixture and stir to combine.

Sprinkle grated Gruyère cheese over the bottom of the partially baked pie shell.

Pour the egg mixture over the cheese.

Bake in the preheated oven for 40-45 minutes, or until a knife inserted into the center comes out clean.

Cover the pie crust edges with foil if they become too brown.

Let the quiche stand for 10 minutes before cutting into wedges and serving.