Cut the meat into pieces of about 1½ cm and brush with the mustard. Heat 2 tablespoons of olive oil in the casserole and fry the meat on a high heat for 5 minutes until golden brown. Sprinkle with salt and pepper to taste and remove the meat from the pan with a slotted spoon.
Heat the remaining olive oil in the pan, add the onion and shallot and stir fry for 3 minutes. Put the meat back in the pan with the thyme, pour the wine and 250 ml water and bring to the boil. Put the lid on the pan and simmer the meat for about 2 hours until fully cooked (longer if necessary). Use the smallest burner on the stove and if necessary, insert a flame distributor. Stir occasionally. Add some extra hot water if necessary.
Halve the radishes. Halve the courgette lengthways and cut into slices. Add the radishes and courgette to the stew when the meat is cooked. Make sure the vegetables keep a bit of a bite. Season with salt and freshly ground black pepper. Put the chard through just before serving, and voila, there you have your Irish Beef inspired colourful stew.