Heat the oil in a pan. 
Brown the sausages in about 8 minutes.
Cut the onions into rings and add them to the sausages after about 3 minutes. 
Melt the butter in another pan. 
Add the flower to the melted butter, stir with a wooden spoon and allow to heat through for about 3 minutes. 
Pour in the milk while stirring with a whisk. 
Let the sauce simmer for about 5 minutes while stirring constantly. 
Season with salt and pepper. 
Switch off the heat and stir in the mustard and finely cut Stilton. 
Cut the broccoli into small florets and boil them for about 3 minutes until soft. 
Put the sausage with onions onto a plate. 
Add the broccoli and pour the cheese sauce on top of the florets. 
Heat the potato mash as described on the product packaging and put it onto the plate beside the sausage.