Cut the steak into 2.5cm squares and divide each kidney into eight pieces.
Line a basin with the suet pastry, leaving some crust to overlap the edge.
Layer the steak and kidney in the basin, seasoning each layer with salt and pepper.
Fill the basin with water until it is 5cm from the top.
Seal the pudding by pressing the crust edges together and folding over the pastry.
Tie the pudding in a floured cloth and boil in water for at least four hours.
Replenish with hot water regularly to keep the pudding submerged and boiling.
Cut a round hole in the top crust before serving to release steam.