In a large skillet over medium heat, heat the olive oil, add the onions, season with salt, and cook, stirring occasionally, until they are deep golden brown and caramelized (40-50 minutes). Stir the beef base into the onions, and set aside to cool.
While the onions are caramelizing, roast a head of garlic. Whisk together the creme fraiche, mayonnaise, onion powder, salt, and thyme, adjusting spices to taste. Set aside until the caramelized onions and roasted garlic have cooled to room temperature. Stir the roasted garlic and 2/3 of the caramelized onions into the sour cream. Transfer to a serving bowl, and top with the remaining onions. Serve with crackers or toast. Better than dehydrated mix!