The humble Jell-O salad and its savory ancestor, aspic, are shaking up American kitchens and even getting a glossy, fine-dining revival. Aspic originally began in medieval kitchens as a way to preserve meat using collagen-rich broths that solidified into savory jelly; it later evolved into a mid-century American status symbol, thanks to pastel Jell-O molds.  But by the 1970s , it fell out of fashion — remembered mostly as an odd mix of mayonnaise, olives and hot dogs suspended in wobbling