Preparation Preheat oven to 400°F. Heat oil in medium skillet over medium-high heat. Add onion. Cover and cook until just tender, stirring often, about 5 minutes. Cool briefly. Whisk cream and next 4 ingredients in bowl to blend. Mix in cheese, chiles, and onion mixture. Pour filling into frozen crust. Bake tart until golden brown and set in center, about 40 minutes.
Preparation Preheat oven to 400°F. Heat oil in medium skillet over medium-high heat. Add onion. Cover and cook until just tender, stirring often, about 5 minutes. Cool briefly. Whisk cream and next 4 ingredients in bowl to blend. Mix in cheese, chiles, and onion mixture. Pour filling into frozen crust. Bake tart until golden brown and set in center, about 40 minutes.