Finely cut the onion and gently fry them in the goose fat until they are translucent.
Cut the peppers into thick strips and put them by the onion. Bake for about 15 minutes, keep stirring occasionally.
Meanwhile, chop the skinned tomatoes into coarse pieces and put to the onion/pepper mixture. Let it simmer for about 20 minutes on low heat. Add piment d'espelette.
Serve with dried ham, e.g. Bayonne ham.