Cut potatoes into bite-sized pieces and soak in water. Drain and place in a microwave-safe container. Cover loosely with plastic wrap and microwave at 600W for about 5 minutes until soft. Mash while hot and mix with the remaining mashed potato ingredients. Let cool slightly.

Season beef slices with salt and pepper, then coat with flour. Place 1/8 of the mashed potato mixture on each slice and roll tightly. Repeat to make 8 rolls.

Heat vegetable oil in a frying pan over medium heat. Place the rolls seam-side down and cook for 3–5 minutes until browned and cooked through. Remove from the pan.

In the same pan, add all sauce ingredients except butter. Heat over medium heat and simmer for about 30 seconds while stirring. Turn off the heat and mix in the butter until melted.