Remove the silver skins from the lamb fillets and place in a freezer bag. Add a few sprigs of rosemary and the pressed garlic cloves. Close the bag tightly and preferably without air. Let it steep in the fridge overnight.
After about 1 hour pass through a sieve and season with salt, pepper and chilli to taste. If necessary, add a few crumbs of granulated broth. Season to taste with the cranberries and, if necessary, bind a little.
Heat the oven to 80 degrees. Heat a pan and briefly sear the fillets on all sides. Let the fillets rest on a wire rack in the oven for about 10 minutes.