Instructions

1. 1
   Mix the starter ingredients together in a small bowl, cover tightly, and set aside in a warm place for 30 minutes.
2. 2
   When the starter is light and bubbly, mix the beer and milk into the mixture.
3. 3
   Put the flour and salt into a food processor, then, with the motor running, add the yeast mixture through the feeding tube. Process the dough until it forms a ball. Add very small amounts of additional flour or milk if necessary.
4. 4
   Process the ball until it is smooth, elastic, and warm, about 45 seconds to 1 minute.
5. 5
   Butter a medium-sized bowl, roll the ball around in the butter, then cover and let rise in a warm place until doubled. Punch down and let rise a second time.
6. 6
   While the dough is rising, heat 1 tablespoon of the oil in a nonstick skillet. Add the onion and cook, stirring, over low heat for 5 minutes or until golden brown. Let cool.
7. 7
   Combine the crème fraîche, salt, pepper, and nutmeg. Add the cooled onion.
8. 8
   Heat the remaining oil in the skillet and fry the bacon until lightly browned, stirring constantly. Remove and drain through a strainer.
9. 9
   Preheat the oven to 450 °F (220 °C) or as hot as it will go. If using a pizza stone, preheat the oven for at least 30 minutes.
10. 10
    Lightly oil a 14 x 16 inch (35 x 40 cm) baking sheet. Roll the dough until slightly smaller than the baking sheet. Place it on the sheet. If using a pizza stone you may roll the dough onto a sheet of parchment paper.
11. 11
    Spread the onion mixture over the dough, leaving a very small raised rim all the way around, then dot with the bacon.
12. 12
    Bake for 4 to 20 minutes depending on oven temperature. The tart should is lightly browned and bubbling. Burned/blackened edges are traditional. Serve very hot.