Ingredients

• A little olive oil (for cooking the mushrooms
• 1 (10 oz) package fresh spinach (I used the baby ones) --- about 284 grams
• 4 eggs (if the yolks are quite small I use 5 eggs)   
• 1 cup shredded cheese of your choice (I use mozzarella or the Italian Blend)   
• 1 (8 oz package) mini-bella mushrooms, chopped   
• 1-2 Tbsp, heavy cream or half-and-half (optional)
• Salt and Pepper, to taste

*Variation - If you don't fancy mushrooms, try asparagus or bell peppers with the spinach. Also, add some onions to the mix. I add some when I do not use mushrooms.
 

Procedure  

Preheat the oven to 375F or 190C.   Heat a little oil in a large skillet. Saute the mushrooms until they are soft, about 5-6 minutes. Set Aside.   Place the spinach in a deep pan or in the skillet that you used for the mushrooms. Add a little water, 1/4 cup should do it. Using medium heat, cook the spinach just until wilted, about 3-4 mins. Use either your hand or a spatula to pack in the spinach. Drain the excess water really well (especially if you decide to use frozen spinach instead).

In a large mixing bowl, whisk the eggs until combined. Add the cooked mushrooms, spinach, cheeses and cream (if using) to the eggs. Mix well. Season to taste. 
Divide evenly among the 12 muffin cups. The muffin tray was slightly bigger than usual so I only filled about 10 cups. Bake for about 20-23 minutes, or until it's well set and a tester/toothpick inserted in the center comes out clean.   Leave in the pan for a few minutes or just until it's cool enough to handle. It was so easy to remove them from the pan! They practically pop-out!