Preheat oven to 400°F (200°C).
Heat oil in a skillet, cook mushrooms 5–6 min, set aside.
In a saucepan, warm cream, garlic, and Gorgonzola (don't boil). Season with salt and pepper.
Layer half the potatoes in a baking dish, add half the cream sauce, half the Gruyère, and half the mushrooms. Repeat layers.
Bake 20–30 min until golden and bubbly.
Rest 10 min before serving.
