Photo: Tara Fisher
Boil the potatoes in a pan of salted water for 15-20 minutes until cooked through.
Meanwhile, heat the olive oil and butter in a 22cm ovenproof frying pan and gently cook the onion for 10 minutes until softened.
Stir in the sliced peppers, smoked paprika and thyme leaves, and cook for a further couple of minutes. Remove from the heat.
Preheat the grill to medium-high. Drain the cooked potatoes and leave them to cool slightly before thickly slicing. Add the potatoes to the pan.
Whisk the eggs in a jug with plenty of seasoning. Over a medium heat, pour the egg mixture over the vegetables in the pan, then tilt the pan to allow the eggs to spread out evenly; cook for 6-8 minutes over a low heat until the egg begins to set. Sprinkle the Manchego pieces on top, then grill for 4-5 minutes, checking regularly, until the top of the frittata is set. Remove from the grill and leave to stand for a minute or two.
Run a spatula around the edge of the pan to loosen the frittata. Slide it onto a board, cut into wedges and sprinkle with thyme sprigs.