Coat each schnitzel with flour, then dip in beaten egg, then coat with breadcrumbs. Season with salt and pepper. Fry in a pan over medium-high heat for 2-3 minutes per side until golden brown. Transfer to a plate.
In the same pan over medium heat, fry the diced onions for 5-7 minutes until translucent. Add the diced bacon and brown mushrooms, cook for 5 minutes until mushrooms are soft. Remove from heat. Season with thyme, basil, salt and pepper. Stir in the sweet cream and grated cheese until combined.
Place the fried schnitzel in a greased baking dish. Pour the sauce over the schnitzel. Cover and refrigerate for at least 8 hours (up to 24 hours).
Preheat oven to 200°C (392°F). Cover the baking dish with foil and bake for 15 minutes. Remove foil and bake for another 15 minutes uncovered until the top is golden.