Ingredients

Makes about 24 diamonds

　　a 1/4-ounce package (about 2 1/2 teaspoons) active dry yeast

　　a pinch of sugar

　　1/4 cup plus 2/3 cup lukewarm water

　　2 3/4 to 3 cups all-purpose flour

　　1 teaspoon salt

　　2 tablespoons olive oil

　　1 pound white or yellow onions, chopped fine (about 3 cups)

　　1/2 cup sour cream

　　2 large eggs

　　1 cup thinly sliced red onion

　　1/3 cup thinly sliced scallion greens

　　1/4 cup minced drained sun-dried tomatoes packed in oil

　　1/3 cup minced Kalamata or other brine-cured black olives

　　

Step 1

In a small bowl proof the yeast with the sugar in 1/4 cup of the water for 5 minutes, or until the mixture is foamy. In a large bowl stir together 2 3/4 cups of the flour, the salt, 1 tablespoon of the oil, the remaining 2/3 cup water, and the yeast mixture until the mixture forms a dough and knead the dough on a lightly floured surface, kneading in enough of the remaining 1/4 cup flour to form a soft dough. Knead the dough for 8 to 10 minutes more, or until it is smooth and elastic, and form it into a ball. Transfer the dough to a lightly oiled bowl, turning it to coat it well, and let it rise, covered loosely, in a warm place for 1 1/2 hours, or until it is double in bulk.

　　

Step 2

In a heavy skillet cook the white onions in the remaining 1 tablespoon oil over moderate heat, stirring occasionally, until they are softened and golden and let them cool. In a bowl whisk together the sour cream and the eggs and stir in the white onions and salt and pepper to taste.

　　

Step 3

Punch down the dough and roll it into a 17- by 13-inch rectangle on a lightly floured surface. Transfer the rectangle to a large baking sheet, with your fingers form a 1/4-inch rim around the edges of the rectangle, and spread the sour-cream mixture evenly over the dough. Scatter the red onion and the scallion greens over half the dough and scatter the sun-dried tomatoes and the olives over the remaining half. Bake the tart in the middle of a preheated 350°F. oven for 25 minutes, transfer it to a rack, and let it cool for 10 minutes. Cut the tart into 2-inch-wide diamonds.