Start by gathering all your ingredients. Chop up the mushrooms, rinse your spinach, and crumble the bacon if you haven't already. Having everything in place makes the cooking smoother.

In a medium skillet, melt the butter over medium heat. Add the mushrooms first. Sauté them until they turn golden brown, about 5-7 minutes. Their flavors will start to emerge, filling the kitchen with a beautiful aroma. Next, toss in the baby spinach. It wilts quickly, so keep an eye on it.

Grab a mixing bowl and whisk the eggs together with heavy cream. This mixture will be the base of your frittata. Be careful! We want everything well combined but not too frothy. The cream adds richness while the eggs provide structure.

Fold in the crumbled bacon and shredded cheese into the egg mixture. The cheese will melt into the dish beautifully, and the bacon gives that irresistible smoky touch.

Pour your egg mixture into the skillet with the sautéed vegetables. Gently stir to distribute everything evenly. Let it cook on the stove over medium heat for about 5 minutes, or until the edges start to set.

Preheat your oven to 350°F (175°C). Once your frittata has begun to set on the edges, transfer the skillet to the oven. Bake for about 20 minutes or until the center is firm and golden.

Once cooked, let your frittata cool for a few minutes. This allows it to set further, ensuring clean slices when you cut into it. Serve warm or at room temperature.