Heat milk to almost simmering. Whisking constantly, add flour-sugar mixture. Cook 5-6 minutes, until thick.
Beat egg yolks and vanilla. Add hot pudding, 1/4 cup at a time, until egg yolks are hot to the touch. Pour egg yolk mixture into pot and whisk vigorously over heat 2-3 minutes. It should be quite thick; thicker than a typical pudding.
Pour cream into ungreased quarter-sheet pan and spread out evenly. Cover with plastic wrap (press plastic down to touch the surface of the cream to prevent a skin from forming) and refrigerate until set and very cold, 3-4 hours or up to overnight.
Dip a butter knife in hot water and run it along the inner rim of the pan to loosen the cream. Invert the pan onto your cutting board to release the cream. Trim edges if necessary and cut cream into diamond shapes.
Place flour in a wide dish. In a second dish, beat eggs and a pinch of salt. Place breadcrumbs in a third dish. Dredge cream pieces in flour, then dip into egg, then into breadcrumbs.
In a skillet, pour oil 1/4-1/2" deep. Heat oil until it almost shimmers. Fry pieces in hot oil until golden brown, turning once, about 3-5 minutes per side.
Combine sugar and cinnamon in a bowl. Sprinkle fried cream with cinnamon sugar as they come out of the pan. Allow to cool slightly before serving. Serve plain or with jam, marmalade or chocolate sauce, if desired.