Place the lamb, onions, carrot, thyme, stock and lentil into a saucepan.
Bring to the boil and simmer for 35-40 minutes or until the lentils and carrots are cooked.
Meanwhile, mix the soft butter and flour together well.
Boil the two potatoes together until very soft, then mash adding the butter salt and pepper.
Once the mince is cooked, turn down to a simmer and mix the soft flour and butter together.
Beat in enough of the butter/flour mix until the mince thickens, then bring to the boil. The mix needs to be fairly thick.
Pour into a casserole dish and cool.
Once cooled, pile on the mash evenly.
Pre heat an oven to 200C gas 6, when ready to eat.
Bake for 25 minutes to brown nicely and warm through.
Serve with sautéed swede see recipe.