"I enjoy flaky pie crust but sometimes I need a little change. The crust is made of whole wheat flour, flax seeds, and poppy seeds, which adds a nice crunch to the creamy spinach and mushroom filling."
Preheat the oven to 375 degrees F (190 degrees C).
Combine whole wheat flour, all-purpose flour, flax seeds, poppy seeds, and salt in a medium bowl. Rub in olive oil. Add enough water to make a pliable dough.
Roll out dough on a floured surface and press into an 11-inch tart pan. Poke holes all over with a fork.
Bake in the preheated oven until the surface of the crust looks dry, about 15 minutes.
Meanwhile, bring a small pot of water to a boil. Add spinach and cook until wilted, 2 to 3 minutes. Drain and cool until easily handled; squeeze out all water and chop.
Heat oil in a large skillet and fry onion for 3 minutes. Add mushrooms and continue sauteeing until tender, about 5 minutes. Transfer to a bowl. Mix in spinach, sour cream, feta cheese, egg, marjoram, salt, and pepper. Spread the filling over the prebaked tart crust.
Reduce the oven temperature to 350 degrees F (175 degrees C).
Bake tart until the center is set, about 50 minutes.