1. Cut the meat into 2 to 3 centimeter cubes.
Coarsely chop the onions and cut the bacon into thick lardons.
2. Melt the butter and sweat the onions in it for 10 minutes to soften them (low heat, covered).
3. Add the bacon, slightly increase the heat, and stir regularly, trying to keep it covered as much as possible.
4. Once the bacon is pink, remove everything (except the juice) and set it aside in a dish.
5. Turn the heat to high and put the meat in the casserole. Stir regularly (do not cover), the meat should brown on all sides and release a fair amount of juice.
Remove the casserole from the heat, transfer the meat to a dish, and keep the juice in the casserole.
6. Dissolve the brown sugar in the meat juice and put it on high heat to reduce it by half.
7. Once reduced, reduce the heat to low and add back the bacon-onion mixture, mixing it with the 'syrup'. Add the meat and mix again, add the bouquet garni and pour in between 80 cl and 1 liter of beer. Season lightly with salt.
8. Gently cover the entire surface with the 'mustard-flavored' gingerbread.
Simmer covered for 3 hours without stirring, until the gingerbread is melted (remove the bouquet after 1 or 2 hours at most).
9. Adjust the seasoning if necessary during simmering.
10. If after three hours the juice is still too liquid, continue simmering with the lid partially open. The sauce should be slightly sticky on the surface but liquid underneath and should not burn at the bottom.