For a side dish to a green salad or a bowl of soup, cut this rich tart into wedges and serve with a plate and fork. For a finger-food appetizer, cut it into small squares and provide napkins. Makes 8 side-dish servings or 16 appetizer servings.
CRUST
2-3/4 cups all-purpose flour
1/4 tsp. salt
1 large egg, beaten
1-1/2 T. olive oil
6 T butter, melted and cooled
1/3 cup cold milk
TOPPING
6 cups thinly sliced yellow onions
3 T. olive oil
1 large egg, beaten
8 ounces Havarti cheese, cut into small chunks
1 cup grated Emmental or Gruyere cheese
To prepare crust: In large bowl, stir together flour and salt; make well in center. Add egg, oil, melted butter and milk to well. Working in the center of well, mix together liquid ingredients, gradually incorporating flour until dough forms. Turn dough out onto floured surface and knead until smooth, about 10 minutes. Form into ball, wrap in kitchen towel, and let stand at room temperature for two hours.
To prepare topping: In large, nonstick skillet, cook onions in oil over medium-low heat until tender but not brown, stirring frequently (This step may take up to 45 minutes. Cooking the onions slowly brings out their full sweetness.) Season with salt and pepper, and cool to room temperature. Mix in egg, then Havarti cheese.
To assemble: Preheat oven to 375 degrees. On floured surface, roll out dough to form a 13-inch round. Transfer to a baking sheet. Fold outer inch of dough over to form a rim. Spread topping evenly over crust. Bake tart 10 minutes, then sprinkle Emmental or Gruyere over. Bake until crust is golden, about 15 to 20 minutes longer. Let cool slightly before cutting.
