Melt 2 to 3 tablespoons of the pork fat in a medium-size skillet over medium-low heat. Add the onions and cook until softened, about 10 minutes. Drain the onions.
Combine the ground veal, ground pork, remaining ground pork fat, coarse salt, pepper, thyme, allspice, tarragon, oregano, garlic, crushed juniper berries, Cognac, Madeira, eggs, and the onions in a bo