The onion cake is a hearty cake that takes its name from main topping, the onions. The cake is popular in southern Germany, eastern Germany and Switzerland as well as in Alsace, France. Depending on what region in Germany you are in, the ingredients and how it is prepared will also change.
420 ml (1 ¾ cups) all-purpose flour
1 ½ teaspoons active dry yeast
2 tablespoons sugar
1 teaspoon salt
3 ½ tablespoons butter
120 ml (½ cup) warm water
1 large, sweet onion
120 ml (½ cup) sour cream
1 teaspoon white pepper
2 teaspoons caraway seeds
Heat oven to 190°C (375°F) and lightly coat 2 baking sheets with oil and set aside.
Combine 240 ml (1 cup) flour, yeast, sugar, and ½ teaspoon salt in large bowl. Melt 3 tablespoons butter and whisk together with 1 egg in medium bowl. Slowly pour butter egg mixture into flour mixture while mixing with wooden spoon.
Add water and continue mixing until thick, wet dough forms. Mix in remaining flour and transfer dough to floured work surface, then knead for 10 minutes until smooth but still somewhat sticky.
When done, transfer dough to lightly oiled bowl, cover with plastic wrap, and set in warm place to rise until doubled in volume, or for about 1 ½ hours.
Place onions and remaining butter in large skillet and cook over medium-low heat, stirring occasionally, until golden brown. Once done, let cool completely.
Whisk together remaining egg, sour cream, white pepper, and remaining salt, then mix together with completely cooled onions.
After dough has doubled in volume, take out and work down dough, then divide into 6 equal portions, each about lemon sized. Press and stretch dough with fingertips to form six 8-inch circles and crimp edges to form ring. Place dough circles on each prepared sheet and top each circle with onion mixture, leaving 1.3 cm (½ inch) free at edges. Lightly sprinkle caraway seeds over tarts.
Bake on middle shelf of oven until golden brown and onion mixture sets, or for about 10 minutes.
Credit: Country Living