►Preheat oven to 400 ̊F.
►FILLING: In a medium skillet, heat 2 tablespoons oil over medium heat until shimmering. Add leeks, salt, and sugar. Sauté, stirring to slowly cook until leeks have caramelized lightly, about 10-15 minutes. Add ground coriander seed and fenugreek and cook another minute. Set aside.
►In large skillet, heat 1 tablespoon oil over medium heat until shimmering.
►Add dandelion greens and fish sauce. Cook 3 to 5 minutes, or until greens have significantly reduced in volume, deepened in color, and given up their moisture. Combine with leek mixture.
►GALETTE: Roll pie pastry into a 9-inch circle and place on a baking sheet. Spoon leek-dandelion mixture into center of crust. Smooth out mixture in flat layer, leaving roughly ½-inch at edges. Fold the edges of the pastry into the middle 6 to 8 times, leaving the filling exposed in the center. Top the filling with 2 tablespoons blue cheese. Bake galette on the middle rack of the oven until crust is golden brown, 25 to 30 minutes.
►Remove galette from oven and cool. Serve topped with additional 2 tablespoons blue cheese and lemon juice.