Pound the beef roulades carefully. Season with salt and pepper, then brush each with 1 teaspoon mustard.
Cut the sheep cheese into small cubes. Chop the olives and garlic cloves. Mix the cheese, olives, and garlic together, then season with thyme.
Preheat the oven to 180°C (350°F).
Place a ham slice on each roulade, then add the cheese and olive filling to the lower end. Fold the long sides inward to contain the filling, then roll up each roulade.
Place the roulades close together in a small casserole dish. Heat the gravy until boiling, then pour it hot over the roulades. Cover the dish.
Braise in the preheated oven at 180°C (350°F) for 50 minutes.
Remove the roulades from the casserole. Stir the sour cream into the sauce with a blender until creamy.