Step #1 Put oven rack in middle position & preheat your trusty oven to 400°F.
Step #2 Very finely grind fennel seeds, & peppercorns in grinder, salt, then rub all over pork.
Step #3 Toss shallots with oil in a 13- by 9-inch flameproof roasting pan, then nestle tenderloins among shallots (without crowding) & roast until thermometer inserted into thickest end of pork registers 155°F, about 30 to 35 mins.
Step #4 Put 2 layers of foil wrap on a work surface & transfer pork to foil wrap.
Step #5 Cool to about room temp, about 1 hr, then wrap in foil wrap & chill until cold, about 2 hrs.
Step #6 While pork cools, put roasting pan with shallots over a burner, then add wine & deglaze pan by boiling, stirring & scraping up any brown bits with a wooden spoon, 1 min.
Step #7 Transfer mixture to a 2- to 2 1/2-quart heavy saucepan.
Step #8 Add cherries, sugar, & rosemary & boil until liquid is reduced to about 2 c, 15 to 20 mins.
Step #9 Discard rosemary sprigs (do not discard any leaves that have fallen off stems).
Step #10 Transfer mixture to a food processor/blender & pulse until coarsely sliced.
Step #11 Use caution when processing hot syrupy napalm-like liquids.
Step #12 Transfer to a bowl & chill, uncovered, until cold, about 1 1/2 hrs.
Step #13 Cut chilled pork with a carving knife or an electric meat slicer diagonally into 3/4-inch-thick slices.
Step #14 Roll up each slice into a cornet (cone) shape & pierce in center with a rosemary sprig to secure.
Step #15 Fill opening of each cornet with about 1/2 tsp cherry sauce (or serve sauce on the side of a big platter of these babies).
Step #16 Note: Pork & cherry sauce can be chilled separately up to 1 day.
Step #17 Cover up cherry sauce after 1 1/2 hrs of chilling.
Enjoy the Pork Cornets With Sour-Cherry Sauce recipe