I’ve made variations of this leek and shallot filling several times, which always ended up in a prepared tart crust. I decided to try making my own crust this time and was glad I did—besides looking kind of fancypants yet rustic, this crust is the perfect compliment to the soft yet textural feel of the caramelized onion blend. A modest sprinkle of brown sugar and vinegar over the leeks and shallots during the hour-long caramelizing process introduces a subtly sweet and tangy quality into this rich and savory tart.
For the filling
2 TB Earth Balance
1 large leek, sliced thinly
4-5 large shallots, sliced thinly
2 TB brown sugar, divided
1 TB vinegar
2 tsp fennel seed
For the roux
1/2 cup Earth Balance
1/2 cup flour
Combine all of the crust ingredients into a Kitchen-Aid mixer. Blend until the dough is smooth and silky, adding a bit more water or flour as needed. Form into a ball and place into an oiled bowl and cover with a damp towel or saran wrap. Let rest for about 30 minutes.
While the dough is resting, melt the Earth Balance in a large skillet over low heat. Add in the leeks and shallots and only stir every 15 minutes. After 30 minutes, add in half of the brown sugar and vinegar. Stir gently and let caramelize for 30 minutes more, adding the rest of the brown sugar and fennel seed during the last 10 minutes. Remove from the heat.
If you are making two tarts, divide the dough into two pieces and roll out on a floured surface as thinly as possible. You can also use a round flat pyrex dish to make one large tart. Lightly spray the baking vessel with a bit of cooking spray, then gently drape the dough into it, leaving the flaps open.
To make the roux, melt the Earth Balance over low heat in a small saute pan and slowly add in the flour. Stir frequently for about 10 minutes, or until a light brown color develops. Pour the roux into the base of the tart. Place the leek and shallot mixture on top of that, then gently gather the flaps of dough and arrange nicely over the top, leaving some of the tart mixture in the center exposed.
Brush the top of the dough with a bit of olive oil and place into a 350-degree oven to bake for about 35 minutes, or until the top is golden brown. Serve immediately.