Fill a roasting pan halfway with water and set on a rack in the lower third of the oven; position another rack in the middle and preheat to 350 degrees F. Wrap the outside (bottom and side) of a 9-inch springform pan with foil. Make the crust: Pulse the graham crackers in a food processor a few times until crushed. Add the walnuts and brown sugar and continue pulsing until finely ground. Add the melted butter, nutmeg and salt and pulse to combine. Press into the bottom and about 1 inch up the side of the prepared pan. Bake until the crust is lightly golden, about 10 minutes. Transfer to a rack and let cool completely.
Make the filling: Beat the cream cheese in a stand mixer with the paddle attachment on medium speed until nearly smooth, about 1 minute. Add the maple syrup and granulated sugar and beat until smooth, about 2 more minutes. Add the eggs, one at a time, beating after each addition. Increase the speed to medium high and beat in the flour, heavy cream, lemon juice and maple extract until the filling is smooth and silky, about 1 more minute.
Pour the filling into the cooled crust. Transfer the cheesecake to the oven, placing it on the middle rack directly over the water bath. Bake until golden and set around the edge but the center still jiggles slightly, about 1 hour 10 minutes. Transfer to a rack and let cool to room temperature, then cover and refrigerate until cold and set, at least 5 hours or overnight. Let the cheesecake sit at room temperature 20 minutes, then run a thin knife around the edge and remove the springform ring.