1Heat oven to 425 degrees F. Combine flour and all-purpose seasoning in pie plate. Coat tenderloins with flour mixture; shake off excess flour and set aside.
2Melt 1 tablespoon oil in Dutch oven or large, heavy oven-safe skillet**, sear pork over medium-high heat for 2-3 minutes or until all sides are lightly brown. Transfer tenderloin to a platter. Repeat with remaining oil and tenderloin. Set tenderloins aside.
3Return pan or skillet to medium heat. Add butter and shallots; cook for one minute until shallots are fragrant. Remove pan or skillet from heat; stir in Calvados and add thyme. Return pan or skillt to heat. Bring to a boil, reduce heat to medium and simmer for two minutes. Remove from heat and stir in 1/4 cup apple cider.
4Return pork to pan or skillet (turning a couple of times to glaze with Calvados mixture) and roast, uncovered, for 20 to 25 minutes or until the internal temperature of the pork reaches 145 degrees F, followed by a 3-minute rest time. While cooking, turn the tenderloins a couple of times to ensure even roasting.
5Transfer to a heated platter and tent with foil. Place Dutch oven or skillet back onto stovetop over medium heat and melt butter. Add apples and onion, scraping off browned bits from the bottom of the pan. Sprinkle with pepper and cook for 5 minutes, stirring occasionally. Spoon onto a plate and once again return pan or skillet to stove.
6Add chicken stock and bring to a boil along with thyme and Calvados. Cook for 3-4 minutes until reduced by a third or to 2/3 cup. Remove thyme. Mix together with the water and cornstarch and slowly whisk into gravy. Slowly stir in cream; cook and stir over medium-low heat for 1 minute. Add apple/onion mixture; cook and stir for 1 minute more. Season with salt and pepper or additional seasoning salt, if desired.