Spoon the mashed potatoes into the mixing bowl of an electric mixer. Add the garlic, egg yolks, paprika and saffron and beat well.
Meanwhile, warm the oil and cream and start adding the oil to the potato mixture while beating on low speed. Add the oil and cream alternately until the sauce has the consistency of mayonnaise. Season with salt and pepper to taste, and beat at high speed for thirty seconds. Serve with poached fish.