The sauce will be thin after braising. You can drizzle it on top of the short ribs as is, but if you'd like to turn it into a thicker gravy, strain the sauce and reserve two cups. Melt 2 tablespoons butter over medium heat in a skillet. Whisk in 2 tablespoons flour and cook for about three minutes, whisking constantly. Slowly pour in the strained sauce. Whisk until smooth. Add a pinch of salt and continue to cook until thickened. This should take a few minutes.