How to Make It
In a medium, deep skillet, cook the sausage over moderately high heat, stirring and breaking up any lumps, until browned, about 8 minutes. Scrape the sausage onto a plate.
In the same skillet, heat the olive oil. Add the onion, carrot and celery, cover and cook over low heat, stirring occasionally, until tender. Add the raisins and vinegar and cook until reduced by half, about 5 minutes. Add the chicken stock and the cooked sausage and simmer over moderately low heat until the stock is reduced by half, about 10 minutes. Remove the sauce from the heat and add the milk; don’t worry if it curdles.
Use an immersion blender to break up the meat and incorporate the milk. Alternatively, transfer the sauce to a blender and blend to a coarse puree, then return the sauce to the pot. Simmer the ragù until thickened, about 5 minutes longer.
The ragù can be refrigerated for up to 5 days.