2 tablespoons vegetable oil
3/4 cup chopped onion
1/4 teaspoon sugar
1 package dry yeast (about 2 1/4 teaspoons)
2 tablespoons warm water (100° to 110°)
1 1/4 cups plain low-fat yogurt
1 tablespoon caraway seeds
1 1/2 teaspoons salt
3/4 teaspoon white pepper
1 large egg, lightly beaten
2 1/4 cups bread flour, divided
1 1/4 cups stone-ground rye flour (such as Bob's Red Mill)
Cooking spray
1 tablespoon water
1 large egg yolk, lightly beaten
1/2 teaspoon kosher salt