Butter a 1½ litre (2 ½ pint) pudding basin or Pyrex bowl and line the base with a disc of non-stick parchment paper. To make the suet pastry, place the suet in a bowl, sieve over the flour and turmeric, then mix gently. Season lightly and then add the water, a little at a time, cutting through the mixture with a round-bladed knife. Use your hands to form a soft dough.
Roll out two-thirds of the pastry on a lightly floured work surface to a ¼ inch thickness and use to line the prepared pudding basin, leaving at least ½ inch of the pastry hanging over the edge. Roll out the remaining piece of pastry to a circle 1 inch larger than the top and set aside.
Place the steak in a bowl with the kidneys. Season to taste and stir in the flour until evenly coated, then mix in the onion, garlic and parsley. Spoon into the lined pudding basin, being careful not to press it down, then pour over the claret and sprinkle the Worcestershire sauce on top. Insert a bay leaf into the middle of the pudding, then carefully pour in enough water to reach about two-thirds of the way to the top, but not covering the meat mixture completely.
Dampen the edges of the pastry lining the basin, place the lid over the filling and press down both edges together to seal. Trim off any excess pastry and make two small slits in the top. Cover the pudding with a disc of non-stick parchment paper and a double piece of foil, pleated in the centre to allow room for expansion while cooking. Secure it with string, making a handle so that you can lift it out of the steamer.
Place the pudding on an upturned (upside-down) plate in a large pan filled two-thirds up the side of the basin with water. Cover and steam for 4-5 hours, adding boiling water occasionally so that the pan doesn’t boil dry. Allow the cooked pudding to stand for 10 minutes, then cut the string and remove the foil and paper. Cover with a flat plate and carefully invert, gently removing the basin.
To serve, peel the paper disc off the top of the steak and kidney pudding and serve straight to the table so that everyone can help themselves.