Heat oil and butter in a larger pan. Add onion and stir. When it crystalizes, add veal and stir again. After browning the veal for a couple of minutes, add bell pepper and stir. Wait a few minutes more and follow up with mushrooms, then tomato and spices. Simmer 10ish minutes.
Heat oven to 490°F (250°C).
Cut 6 10x10 squares out of foil (or parchment/ baking paper). Place all on a working area and fill equally with the sauce. Add two tablespoons of heavy cream to each. Wrap them up into small bags by lifting the sides up toward the middle first, and then pinching them together on sides (they'll resemble a Hershey Kiss after you're done). (If you're using parchment paper you can tie the bags together with a small amount of rope.) The bags should be completely sealed as to not let anything in or out.
Place the bags into a deep baking pan. Fill it up with hot water about half the height of the bags. (You're essentially making a water bath.) Bake for 30 minutes. Lower temperature to 390°F (200°C). And bake another 40 minutes. Keep the level of water by adding more hot water if necessary. Turn the pan around at least once during the water bath.
When ready to serve, give each person a bag (careful, it's hot!) on a plate, and let them open it on their own.