Crustless Spinach & Asparagus Quiche with Gruyère

Preheat oven to 375°F. Coat a 9-inch deep-dish pie pan with cooking spray.

Heat oil in a large nonstick skillet over medium heat. Add onion and cook, stirring often, until translucent, 2 to 3 minutes. Increase heat to medium-high and add asparagus; cook, stirring often, until the asparagus is tender-crisp, 3 to 4 minutes. Add spinach, thyme and garlic; cook, stirring constantly, until the spinach is wilted and the garlic is fragrant, 1 to 2 minutes. Remove from heat and let cool for 10 minutes.

Whisk eggs, half-and-half, mustard, salt and pepper in a medium bowl. Gently stir in the asparagus mixture and cheese; spoon into the prepared pie pan. Place the quiche on a rimmed baking sheet and bake until set and golden brown around the edges, 30 to 35 minutes. Let stand for 10 minutes before slicing.