8 potatoes (such as Maris Piper), peeled and cut into large chunks
500g/1lb 2oz spinach, washed
225g/8oz plain flour
salt and black pepper
200g/7oz black treacle
3-4 tbsp vegetable oil
2 knobs of butter
4 free-range eggs
350ml/12fl oz milk
1 x 800g/1lb 12oz fillet of beef (a middle cut such as rib or loin), at room temperature
500ml/18fl oz red wine sauce or gravy, to serve