From Daringgourment.com

I had this tart years ago when I was visiting Baden-Baden.  It was so good I never forgot it.  The other day I had loads of onions sitting around so I googled it and found this fantastic recipe and have since made it a few times.  Because I have such limited space here you can find the crust recipe on our website, but you can also use bought pie crust.  For GF folks I have also made this gluten free using a polenta tart dough recipe from Jamie Oliver. 

The Dough:

1/2 cup plus 2 TB Eatwell Farm Heirloom Flour

1/2 tsp Salt

4 TB Butter at room temp, cut into small cubes

A little less than 1/2 cup warm Milk (start with about 1/3 and add more if necessary)

1 tsp Yeast

To make the dough dissolve the yeast in the warm milk and let stand for 5 minutes.  Place the flour and salt in a stand mixer and make a well in the center.  Add the butter and pour the milk mixture over.  Using a dough hook, knead the dough on the “bread” setting for about 6 minutes.  Add more milk or flour as needed.  Form the dough into a ball, spray the same bowl with olive or vegetable oil, cover loosely with plastic wrap, and let the dough rise in a warm place until nearly doubled in size. 

The Filling:

2 TB Butter

2 1/4 lbs Onion, finely diced

5 slices thick cut Bacon, finely diced

1 1/2 cups full fat Sour Cream

4 Eatwell Farm Eggs

2 TB All-Purpose Flour

2 tsp Salt

1 tsp Caraway Seeds

Freshly ground Black Pepper

Fry up the bacon.  When the bacon is done add the onions to it along with 2 TB of butter.  Reduce the heat and let the onions slowly caramelize to a nice golden brown, about 30-40 minutes.  Remove from heat and allow the mixture to cool.  In a bowl, combine sour cream, eggs, flour, salt and caraway seeds, and some freshly ground pepper.  Add the onion/bacon mixture to it and thoroughly combine everything.  If using refrigerated pie crust, grease the springform and gently press the crust into the pan, leaving about 1/2 inch or so margin along the top.  If making the dough yourself, once the yeast dough has risen, butter a medium-sized springform (9” or so) and spread out the yeast dough on the bottom and up the sides (leaving about 1/2” from the top).  The dough will keep retracting, just work fairly quickly and then immediately pour the onion mixture into it (it will hold the dough in place), and put it in the oven.  Place the Zwiebelkuchen on the middle shelf in the oven preheated to 400 F and bake for 55 to 60 minutes, until the top is light brown and the center of the pie feels fairly firm to the touch.  Let cool for at least 20 minutes before serving.  Can be eaten lukewarm or cold.