Blanch the turnip slices in boiling, salted water for a minute. Drain.
Place the turnip slices in a saucepan along with half the butter. Cook over medium heat, stirring frequently for a few minutes. Do not let the turnips brown.
Add the stock, bread crumbs, sugar, nutmeg, and pepper. Cook, covered, over low heat until the turnips are soft, about 25 minutes.
Purée the turnips in a food processor. Place the purée in a bowl along with the glace, cream, the remaining butter, and some salt. Stir to combine all the ingredients. Optional: pass the purée through a strainer.