In a food processor, combine flour, salt and margarine and process for about five seconds. Sprinkle the ice water over the flour mixture and pulse until pastry just begins to come together, about 10 seconds; you should still be able to see small pieces of margarine in it.

Transfer the pastry to a work surface, gather it together and pat into a disk. Wrap the pastry in plastic and refrigerate until chilled. (You can also roll out the pastry and use it right away.)

In a large skillet over high heat, heat two tablespoons oil.

Add onions; cook four to six minutes, stirring, until translucent. Add cabbage and 1/2 teaspoon salt. Reduce heat to medium and cook, stirring often, for 10 minutes.

Then reduce heat to low, cover and continue cooking until reduced and golden, 40 to 50 minutes. Taste and add salt and pepper as needed.

Dice mushrooms. Heat remaining two tablespoon oil in another large skillet over medium-high heat. Cook garlic, stirring, for one minute. Add mushrooms, and remaining salt.

Cook, stirring often, until the mushrooms are tender and begin to brown, about 10 minutes. Add wine; cook, until it evaporates, about one minute. Add mushrooms to the cabbage. Cool.

Preheat oven to 400 degrees Fahrenheit. On a sheet of Gefen Parchment Paper, roll the dough out into a 15-inch circle. If it cracks a bit, just press the pieces together. Dust with flour as needed and keep the circle as even as you can, but don’t worry about rough edges.

Spread the cabbage-mushroom mixture over the pastry, leaving a two-inch border. Use the parchment to lift the edges of the pastry and fold loosely over the filling in two- or three-inch sections. It may crack as you fold it but that’s fine. Transfer the galette, on the parchment, onto a baking sheet.

Bake the galette for 35 to 40 minutes. Let cool at least 15 minutes on the baking sheet. Lift parchment and galette onto a platter; gently pull the parchment out. Serve warm or at room temperature.