How to Make It
Preheat oven to 350°F. Grease bottom and sides of a 9-inch springform pan with softened butter. Wrap underside and outside in a double layer of aluminum foil.
Place graham crackers, brown sugar, and salt in bowl of a food processor. Pulse until combined, about 3 times. Add melted butter, and pulse until fully incorporated, about 10 times. Press crust evenly onto bottom of prepared pan, and bake in preheated oven until crust is lightly browned, about 15 minutes. Transfer to a wire rack, and cool completely, about 30 minutes.
While crust cools, combine cream cheese, sour cream, and granulated sugar in bowl of a stand mixer. Beat on medium speed until smooth, 4 to 5 minutes, stopping to scrape sides of bowl as needed. Reduce speed to medium-low, and add eggs and egg yolk, one at a time, beating well after each addition. Stir in vanilla. Pour filling over crust, and smooth top.
Place springform pan in a roasting pan. Add boiling water to roasting pan to reach halfway up sides of springform pan. Bake in preheated oven until top is lightly browned and cheesecake is set around edges but still jiggly in middle, 1 hour to 1 hour and 15 minutes. Remove cheesecake from water bath, and transfer to a wire rack to cool completely, about 2 hours. Remove foil around pan, and discard. Cover cheesecake in pan with plastic wrap, and chill at least 8 hours or up to 4 days.
Stir together marmalade and 1 tablespoon water in a small saucepan. Cook over low, stirring occasionally, until marmalade has slightly loosened, 3 to 5 minutes. Remove sides of springform pan from cheesecake, and slice cheesecake. Spoon marmalade over cheesecake slices, and garnish servings with grapefruit supremes.