1/4 cup (1/2 stick) unsalted butter
1 teaspoon extra-virgin olive oil
2 large onions (about 1 1/3 pounds total), halved through root end, thinly sliced lengthwise
Fine sea salt
1 16-ounce container sour cream
1 8-ounce container crème fraiche
1/2 cup fromage blanc or cream cheese
3/4 teaspoon ground chipotle chile powder
Garlic Pita Chips
Melt butter with olive oil in heavy large skillet over medium-high heat. Add onions; sprinkle lightly with sea salt and saute until onions begin to turn golden brown, stirring frequently, about 15 minutes. Reduce heat to medium and continue to saute until onions are deep golden brown, about 10 minutes longer. Remove from heat and cool onions to room temperature.
Combine onions, sour cream, crème fraiche, fromage blanc, and chipotle chile powder in large bowl; mix until well blended. Season to taste with fine sea salt and freshly ground black pepper. Transfer to serving bowl. Cover; chill at least 1 hour. DO AHEAD: Can be made 1 day ahead. Keep refrigerated.
Serve with Garlic Pita Chips.