Whisk eggs, egg yolks, ¾ cups sugar, and orange zest in a large heatproof bowl.
Bring 2 cups heavy cream, milk, cloves, star anise, cinnamon sticks, and cardamom pod to a simmer in a large saucepan over medium heat; slowly whisk into egg mixture.
Steep 30 minutes. Strain.
Whisk in vanilla extract and pumpkin purée. Chill 3 hours.
Stir 1 cup sugar and ¼ cup water in a small heavy saucepan over low heat until sugar dissolves.
Increase heat; boil without stirring until syrup is deep amber, brushing down sides of pan with a wet pastry brush and swirling pan occasionally, about 10 minutes.
Stir in ⅓ cup heavy cream (caramel will bubble vigorously).
Divide caramel among ramekins; chill until set.
Divide custard among ramekins; place in a large pan.
Add hot water to pan to come halfway up sides of ramekins; cover pan with foil.
Bake at 350° until center is just set, 20–25 minutes.
Chill until cold. Invert onto plates.
