Pork Cornets With Sour-Cherry Sauce

Put oven rack in middle position and preheat oven to 400u0b0F.
Very finely grind fennel seeds, salt, and peppercorns in grinder, then rub all over pork.
Toss shallots with oil in a 13- by 9-inch flameproof roasting pan, then nestle tenderloins among shallots (without crowding) and roast until thermometer inserted into thickest end of pork registers 155u0b0F, about 30 to 35 minutes. Put 2 layers of foil on a work surface and transfer pork to foil. Cool to room temperature, about 1 hour, then wrap in foil and chill until cold, about 2 hours.
While pork cools, put roasting pan with shallots over a burner, then add wine and deglaze pan by boiling, stirring and scraping up any brown bits with a wooden spoon, 1 minute. Transfer mixture to a 2- to 2 1/2-quart heavy saucepan. Add cherries, sugar, and rosemary and boil until liquid is reduced to about 2 cups, 15 to 20 minutes. Discard rosemary sprigs (do not discard any leaves that have fallen off stems). Transfer mixture to a food processor and pulse until coarsely chopped. Transfer to a bowl and chill, uncovered, until cold, about 1 1/2 hours.
Cut chilled pork with a carving knife or an electric meat slicer diagonally into 3/4-inch-thick slices. Roll up each slice into a cornet (cone) shape and pierce in center with a rosemary sprig to secure. Fill opening of each cornet with about 1/2 teaspoon cherry sauce. Discard rosemary sprigs when eating.