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Preheat oven to 400 degrees.
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Remove the dough from the refrigerator and let it warm up just enough to roll out.
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Sprinkle with a little flour and roll out the dough to no more than 1/4 inch thick.
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Sprinkle the gruyere on top, leaving about 1 1/2 inches clear around the edge of the dough.
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Arrange potato slices on top of the gruyere then with your hands break the gruyere/mascarpone mix into small pieces and spread around.
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Evenly sprinkle on 1/3 of the onions and sage and top.
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Repeat 2 more times.
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Gruyere, potato, gruyere/mascarpone mix, onions and top with any remaining gruyere and sage.
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It doesn't need to be exact as it will all end up in there anyway. But I do like to make sure to have some gruyere and sage for the top.
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Lastly, top with the whole sage leaves.
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Bake on middle rack for 30 to 40 minutes or until it becomes golden.