Mashed potato with butter, sugar, lemon and egg, baked. The term 'cheese' may derive from the earlier usage meaning 'moulded', as with fruit 'cheeses'. (Rundell 1807, etc)

Original Receipt in 'A New System Of Domestic Cookery' by 'A Lady' (Mrs. Maria Eliza Ketelby Rundell) (Rundell 1807);

POTATO CHEESECAKE. - E. R.
Two ounces of butter, the same of pounded sugar, and six ounces of potatoes boiled and floured through a sieve, the rind of one lemon, and half the juice, unless acid is desirable; mix these ingredients well together, with two eggs, and fill the tart-pan and bake it.