Preheat oven to 350℉
In a large bowl, whisk together eggs, cream, salt, and pepper until fully combined. Set aside.
Heat a large oven-safe skillet over medium heat.
Add diced pancetta and cook until crisp and golden, about 4–5 minutes. Remove and set aside, leaving the pancetta fat in the pan.
Add mushrooms to the same skillet. Cook without stirring too much at first so they can brown properly, about 5–7 minutes.
Add shallot and thyme and cook another 1–2 minutes until fragrant.
Lower heat to medium-low. Return pancetta to the skillet and stir gently to distribute.
Pour the egg mixture evenly over everything.
Grate half of cheese into egg mixture and combine well.
Let the frittata cook on the stovetop for 2–3 minutes until the edges begin to set.
Transfer the skillet to the oven and bake for 12–15 minutes, until the center is just set but still slightly soft.
Let rest for 5–10 minutes before slicing. Serve warm.
