Makes: 12 servings
Place the flour, egg, egg yolk and salt in a food processor. Cover and pulse until blended. Add butter; cover and pulse until butter mixture resembles the size of coarse peas. Drizzle in water; pulse until dough forms a ball. Cover with plastic wrap. Refrigerate at least 2 hours. Remove dough from refrigerator 30 minutes before preparing tarts.
Sauté onions in butter, in batches, in a large skillet over medium-high heat until tender. Cool completely in a large bowl. Whisk eggs, egg yolks and cream in a small bowl. Stir into onions; add the cheddar, bacon and chives. Season with salt and pepper. Set aside.
Heat oven to 350°F. Divide dough in half. Roll out one portion on a lightly floured surface. Press dough onto bottom and up sides of an ungreased 10-inch tart pan with removeable bottom. Prick dough with a fork. Repeat with remaining dough. Bake each crust for 5-8 minutes or until just golden brown. Remove from oven. Divide onion filling into crusts. Bake for 15-20 minutes longer or until a thermometer reads 160°F and egg mixture is set. Let stand 5 minutes before serving. Cut into wedges.