Rustic Onion Galette

On one of my last evenings visiting home with Mom, I made an onion tart, or more accurately an onion galette, that was inspired by some fresh red onions bought in a farm produce market in the Valley. This recipe makes two small galettes, 6-7 inches in diameter, but you could also make a single larger one. Serve with a green vegetable and/or a salad. (We ate it with Chickpea Salad with Roasted Red Peppers)

Sources: The crust comes from  3-Onion Leek Tart by Kelly of Sass & Veractiy, and the filling from Onion Tart with Mustard and Fennel by Deb Perlman of Smitten Kitchen.
Servings: 4 as a main course, more if you cut it into wedges for appetizers

Crust:

3 tablespoon buttermilk
1/3 cup ice water
1 cup flour
1/4 cup cornmeal
1 teaspoon sugar
l pinch salt
7 tablespoons cold unsalted butter, chunked

Filling:
3 red onions, cut in half and thinly sliced
2 teaspoons olive oil
1 teaspoon fennel seeds
1/2 treaspoon salt
1/4 teaspoon ground pepper
2 teaspoons grainy French or Dutch mustard
1/2 cup grated Gouda cheese


To make the crust:

1. Mix the buttermilk and ice water in a small nowl and keep it cold.  
2. In a medium bowl, mix the flour and cornmeal, then pinch in the butter with your fingers until the mixture resembles a coarse meal of uneven sized crumbs.  
3. Sprinkle a bit of the buttermilk-water mixture over the meal a bit at a time and mix lightly with a fork until it begins to hold together. Only add as much liquid as needed to form a soft but not sticky dough.   (You probably won't need all the liquid.) 
4. Gather the dough into a ball and flatten it, wrap well in plastic and refrigerate for at least 2 hours.

To make the filling: 

1. Heat the oil in a skillet until it shimmers. 
2. Add the fennel seeds, cooking until a shade darker, about 30 seconds. 
3. Add the onions, salt, and pepper. Reduce the heat to medium-low and cover, cooking for about 30 minutes, stirring occasionally, until onions are very tender and golden brown.

To assemble:

1. Preheat the oven to 400 F.
2. Take the cold dough, divide it in two, and roll out two rounds of about 12 inches in diameter. You can leave the edges rough--this is a rustic tart!
3. Place a round of dough on a baking sheet.
4. Spread a teaspoon (or slightly more) of mustard over the center of the dough.
5. Spoon half of the filling into the center, spreading it to leave 3 inches of dough free at the edge.
6. Sprinkle with half of the grated cheese.
7. Fold the edge over the filling, forming pleats in the dough and leaving the center open.
8. Repeat for the second tart. You should be able to fit both galettes on one baking sheet.
9. Bake for about 40-45 minutes until the crust is golden.