Peel the potatoes and pre-cook them for 15 mins. Remove the princess beans from the freezer to defrost. Collect the defrost water separately.
Heat the grill directly.
Dice the onions for the sauce. Place the Dutch oven in the grill. Add the butter and a little oil and fry the onions in it. Add a pinch of sugar. Dust with flour and brown. Deglaze with the vegetable stock. Pour in the cream and reduce briefly. Stir in the spices.
Add the cooked potatoes, beans and mushrooms to the sauce and sprinkle with the gratin cheese.
Set the grill to indirect using the deflector stone. Cook the gratin for approx. 45 mins. with the lid closed.
Enjoy your meal!