Cut the butter into small pieces. In a heavy 4 quart saucepan, melt it over high heat until foamy. Be careful not to burn it. Stir in the gravy, onion, spices. Reduce the heat to low, but do not cover. Simmer the mixture for 45 minutes, stirring frequently. Pour the mixture into a jar through a sieve lined with several layers of cheese cloth. Strain the oil repeatedly until it is clear. Any spices or solids that remain will turn the oil rancid. Cover the oil and store in the refrigerator for up to 6 months.