Simmer wine, stock, and balsamic vinegar in a large saucepan until reduced by half.
Preheat the oven to 200°C.
Line Yorkshire pudding tin holes with layers of thinly sliced potatoes, melted butter, seasoning, and chopped prunes.
Bake the potato cakes for 30 minutes until cooked, then cool slightly and remove from the tin.
Fry the seasoned beef fillets in butter and oil for 5-6 minutes per side.
Remove the steaks from the pan and rest them in a warm place.
Wilt spinach in the same pan, then remove and sauté vegetables and parsley before adding back the sauce and butter.
Serve the steak on a bed of spinach and potato cakes, topped with the vegetable sauce.