Heat oil in medium skillet over medium-high heat. Add onion and cook, flipping occasionally, until onion is lightly browned and oil absorbs flavor from onion, about 5-7 minutes; discard onion, retaining oil in pan.
Add refried beans to skillet with oil. Cook, stirring often, until oil is absorbed and beans are heated through, about 3 minutes; remove beans from heat and keep warm.
In medium bowl, stir together sour cream, heavy cream and salt; set aside.
To assemble, spread refried beans onto warm tortillas; drizzle with sour cream mixture, sprinkle with cheese and top with desired garnishes. Serve immediately.