Eggnog Flan on Cinnamon Crust

Ingredients:
1 cup all purpose flour
1/2 teaspoon (generous) ground cinnamon
1/8 teaspoon (generous) freshly grated or ground nutmeg
1/8 teaspoon (generous) salt
1 large egg yolk
1 tablespoon whipping cream
6 tablespoons (3/4 stick) unsalted butter, room temperature
3 tablespoons sugar
1 3/4 cups sugar, divided
1/3 cup water
1 tablespoon light corn syrup
6 large egg yolks
2 large eggs
2 cups heavy whipping cream, divided
2 cups whole milk
2 tablespoons dark rum
1 tablespoon freshly grated or ground nutmeg
1 cup chilled heavy whipping cream
1/4 cup powdered sugar
1 tablespoon dark rum
3/4 teaspoon vanilla extract
Freshly grated or ground nutmeg (for sprinkling)

Instructions:
Whisk first 4 ingredients in small bowl to blend. Whisk egg yolk and 1 tablespoon whipping cream in another small bowl to blend. Using electric mixer, beat butter and sugar in medium bowl until blended. Beat in yolk mixture (mixture may look curdled). Beat in flour mixture just until blended (dough will be slightly sticky). Using floured hands, gather dough together and form into disk. Wrap in plastic; chill at least 1 hour. DO AHEAD: Can be made 1 day ahead. Keep chilled. Let soften slightly at room temperature before rolling out.
Position rack in center of oven and preheat to 375°F. Roll out dough on lightly floured parchment paper to 9-inch round. Using 8 1/2-inch-diameter plate as guide, cut out round. Transfer dough round, still on parchment, to baking sheet. Pierce dough all over with fork. Bake until crust is golden brown and baked through, 28 to 30 minutes. Cool crust completely on baking sheet. DO AHEAD: Can be made 1 day ahead. Cover and store at room temperature.
Combine 1 cup sugar, 1/3 cup water, and corn syrup in heavy medium saucepan. Stir over medium-low heat until sugar dissolves. Increase heat and boil without stirring until mixture turns deep amber, occasionally swirling pan and brushing down sides with wet pastry brush, about 10 minutes. Immediately pour caramel into 9-inch-diameter cake pan with 2-inch-high sides. Using oven mitts to protect hands, tilt pan to swirl caramel over bottom and halfway up sides of pan. Cool while preparing custard.
Position rack in center of oven and preheat to 325°F. Whisk egg yolks, eggs, 1 cup cream, and 1/4 cup sugar in large bowl to blend. Combine 1 cup cream, milk, rum, nutmeg, and 1/2 cup sugar in large saucepan. Stir rum mixture over medium heat until sugar dissolves; increase heat and bring to simmer. Gradually whisk hot rum mixture into yolk mixture. Pour mixture through fine strainer into cake pan with caramel. Place cake pan in large roasting pan. Add enough hot water to roasting pan to come halfway up sides of cake pan. Cover roasting pan loosely with foil.
Bake flan until set, about 1 hour 40 minutes (center may move slightly when pan is gently shaken, but top will feel set when lightly pressed). Remove from oven; let flan stand in roasting pan with water 10 minutes. Remove cake pan from roasting pan. Transfer directly to refrigerator; chill uncovered overnight. DO AHEAD: Can be made 2 days ahead. Cover and keep chilled.
Combine all ingredients except nutmeg in large bowl. Using electric mixer, beat until peaks form. DO AHEAD: Can be made 2 hours ahead. Cover and chill. Rewhisk to thicken, if necessary, before using.
Run small knife around flan to loosen from pan. Place baked crust atop flan in pan. Place large platter atop flan with crust. Using both hands and holding platter and pan with flan firmly together, invert flan with crust onto platter. Scrape any caramel remaining in pan over flan. Top center of flan with mound of rum whipped cream. Sprinkle cream lightly with grated nutmeg.