Preheat the oven to 450 degrees F. Heat the butter in a large saute pan over high heat. Add the granulated sugar and stir until it dissolves. Add the peaches and cook, stirring, until the sugar starts to turn dark amber in color, 5 to 6 minutes. Add the brandy, carefully ignite it, and flambe the peaches. Remove from the heat and allow to cool for about 10 minutes. In a large mixing bowl, combine the heavy cream, eggs, brown sugar, cinnamon, and nutmeg and whisk until smooth. Fit the rolled-out dough into a 9-inch pie pan, trimming and crimping the edges. Spoon the peach mixture into the piecrust. Place aluminum foil around the crust to prevent it from browning too much, then bake for 30 minutes. Remove the foil, then pour the cream mixture over the peaches. Bake until the custard sets, about 1 hour. Remove from the oven and let cool for about 20 minutes. To serve, place a slice of the pie on each plate and garnish with the confectioners' sugar, mint sprigs, and whipped cream.