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1
For the crust: In a food processor combine the flour, salt, and sugar.
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2
Pulse to combine.
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3
Add the butter and pulse until the butter is finely chopped and the mixture resembles a coarse meal.
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4
Add the mascarpone cheese and lemon juice and pulse a few times.
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5
Add the ice water and run the machine just until the mixture is moist and crumbly, but does not form a ball.
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6
Do not over mix.
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7
Turn the dough out onto a sheet of plastic wrap.
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8
Press into a disc, cover, and refrigerate for 30 minutes.
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9
For the filling: Place an oven rack in the lower third of the oven.
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10
Preheat the oven to 400 degrees F. Melt the butter in a large nonstick skillet over medium heat.
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11
Add the apple slices, sugar, and cinnamon.
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12
Cook, stirring frequently, until the apples are softened, but not mushy, about 5 minutes.
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13
Set aside to cool for 10 minutes.
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14
Stir in the lemon juice, lemon zest, walnuts, and Gorgonzola.
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15
Cut a piece of parchment paper to fit the inside of a 12 by 17-inch baking sheet and place on a work surface.
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16
Place the chilled dough on the parchment paper.
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17
Roll the dough out into an 11-inch circle, about 1/4-inch thick.
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18
Lift the parchment paper and transfer to the baking sheet.
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19
Spoon the apple filling into the center of the dough.
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20
Spread the filling evenly, leaving a 2-inch border.
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21
Fold the dough border over the filling to form an 8-inch round.
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22
Pleat the edge of the pastry and pinch to seal any cracks in the dough.
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23
Using a pastry brush, brush the crust with the beaten egg.
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24
Bake until the crust is golden, about 25 minutes.
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25
Cool for 10 minutes before slicing and serving.
