Preheat the oven to 350ºF. Grease a 9" square baking dish or any casserole-style dish with ghee.
In a large skillet over medium heat, cook the sausage until broken into crumbles and just browned.
Add the chopped veggies and 2 Tbsp of ghee, and cook until the vegetables are soft (about 10 minutes).
Stir in the chopped chestnuts or hazelnuts, and the herbs and spices. Season with additional salt & pepper to your liking.
Add the almond flour and whisked eggs, and stir until completely mixed.
Pour into to the greased baking dish, and smooth over the top.
Transfer to the oven and bake for 45 minutes or until golden brown & crispy on top.