Combine first 5 ingredients in large, deep nonaluminum bowl.
Add pork, covering completely with marinade.
Refrigerate 2 to 3 days, turning daily.
Heat 3 tablespoons butter in large skillet over medium-low heat.
Add onion, cover and cook until soft and transparent, about 15 minutes.
Increase heat to high, sprinkle onion with sugar and continue cooking, stirring constantly, until golden, about 5 minutes.
Remove from heat and sprinkle with salt (onion can be prepared up to 1 day ahead).
Remove pork from marinade; rinse gently under cold water and pat dry with paper towels.
Heat remaining clarified butter in heavy 4 to 5 quart nonaluminum saucepan over medium-high heat.
Add pork and brown well on all sides, about 15 to 20 minutes.
Remove pork and pour off all fat in pan.
Add stock to pan, scraping up any browned bits clinging to bottom.
Return pork to pan with onion, 1/4 cup vinegar and garlic and bring to gentle simmer.
Cover and cook until pork is tender and meat thermometer inserted in thickest part registers 165°F, about 1 1/2 to 2 hours.
(Can be prepared up to 1 day ahead to this point and reheated.) Transfer pork to cutting board and slice thinly.
Cover and keep warm.
Skim any fat from pan juices.
Stir in cream (onion should be just moist; if sauce is too thin, reduce over high heat).
Taste and adjust seasoning with salt, pepper and Sherry vinegar (onion should be tart-sweet).
Arrange pork slices on heated platter and dollop with some of onion mixture.
Spread remaining mixture around edge of platter.
Sprinkle pork with nuts and raisins and serve.