Preheat oven to 350°F (175°C). Lightly spray a 12-cup mini muffin tin with non-stick cooking spray.

Clean and slice about 1 cup mushrooms; chop smaller if you like smaller bites.

Heat a tablespoon of oil or butter in a skillet over medium heat. Sauté mushrooms until golden and most moisture has evaporated, about 6–8 minutes. Season lightly with salt and pepper.

Add chopped spinach to the pan for the last 1–2 minutes just to wilt. Remove from heat and cool slightly.

In a bowl, whisk 6 large eggs until blended. Whisk in 1/2 cup milk and 1/4 cup heavy cream until smooth. Stir in 1/4 teaspoon garlic powder and salt and pepper to taste.

Place a small spoonful of mushrooms and spinach into each greased muffin cup (about 1–2 teaspoons).

Sprinkle about 1 tablespoon of shredded cheddar into each cup over the veggies.

Carefully pour the egg mixture into each cup, filling nearly to the top but leaving a little room for expansion.

Bake in the preheated oven for 15–18 minutes, or until the centers are set and tops are lightly golden. A toothpick inserted should come out mostly clean with a few moist crumbs.

Let quiches rest in the tin 3–4 minutes, then run a small knife around edges and lift out onto a rack to cool slightly.

Garnish with chopped fresh parsley. Serve warm or at room temperature. If serving later, cool completely first, then refrigerate.

If you want a slightly crisper top, broil for 30 seconds at the end—watch carefully.