Peel the grapefruit so that the white skin is removed. Cut out the pulp between the parting skins. Collect the juice. Peel and finely chop the onions. Heat the oil in a pot and fry the onions for about 5 minutes at medium heat until golden brown. Wash and add the cranberries.
Add sugar, mustard seeds and bay leaves and mix. Let it braise at low heat for 3-4 minutes while stirring occasionally. Pluck thyme leaves from the stalk and add to the cranberries. Deglaze with raspberry vinegar and grapefruit juice and let it boil down for 8-10 minutes at low heat while stirring occasionally. Add the grapefruit fillets and cook for another 3 minutes. Pour into 3 glasses (each containing approx. 250 ml) and close well