Cook the potatoes in boiling water for 12–15 minutes, until tender. Meanwhile, cook the peas in boiling water for 3 minutes until tender.
Heat 1 tablespoon of the oil in a frying pan over a medium heat, add the lamb and brown on all sides for 2–3 minutes. Remove the lamb from the pan and place on a baking sheet.
Mix together the breadcrumbs and mint and season with salt and pepper.
Spread the fat side of each rack with the mustard and then press on the breadcrumb mixture. Sprinkle with the remaining oil and bake in a preheated oven, 200˚C (400˚F), Gas Mark 6, for 12–15 minutes, until golden (or longer if you prefer your lamb less pink).
Drain the potatoes and peas, then mash with the butter and crème fraîche. Season well with salt and pepper.
Remove the lamb from the oven and cut each rack in half.
Divide the mash between 4 warmed plates and top with the lamb. Serve with redcurrant jelly.