Beet Greens Galette

1 pound washed and destemmed beet greens
2 tablespoons olive oil
1/2 pound sweet onion, coarsely chopped
3 cloves garlic, minced
1 egg, separated
1/4 cup creme fraiche or cream
nutmeg, salt, and pepper to taste
2 ounces grated Gruyere
Pastry dough for a single crust

Put the wet beet greens in a large saute pan over medium heat. Cover and cook, tossing occasionally, until wilted. Transfer to a colander to drain and cool.

Wipe out the pan and return to the heat. Add the olive oil to the pan and saute the onion and garlic until the onion is translucent. Turn the heat down to low and continue to cook, stirring occacionally, until the onion just starts to turn golden.

While the onion is cooking, squeeze the moisture out of the beet greens by the fistful. Coarsely chop the greens.

Once the onion has turned slightly golden, add the chopped greens and stir to mix for a couple minutes. Remove from the heat and allow to cool.

Mix together the creme fraiche, egg yolk, nutmeg, salt and pepper. When the onion and greens mixture has cooled stir them into the creme fraiche mixture.

Roll the pastry dough into a 14 to 16-inch circle. Put the sheet of dough on a piece of parchment paper or an unrimmed baking sheet. Spread the greens mixture in a 12-inch circle in the middle of the dough. Sprinkle the cheese evenly over the greens. Pull the edges of the dough up over the filling letting the dough fall into casual pleats. Lightly beat the egg white and brush the top of the dough with it. Bake the galette in a 400ºF oven for about 30 minutes. I like to bake it for 20 minutes on a pizza stone set on the floor of the oven, and then for another 10 minutes higher in the oven to brown the top.