In a medium saucepan, whisk together whole milk, heavy cream, dark brown sugar, cornstarch and molasses. Constantly whisk over medium heat until it reaches a simmer, and the mixture slightly thickens. Remove from heat. The cornstarch will initially look lumpy, but keep whisking, and it'll smooth out. Do not boil. 

In a small bowl, whisk the egg yolks with vanilla extract, ginger, cinnamon, nutmeg and cloves for about three minutes. Add a ladle of the cream mixture to yolks and whisk constantly. Once it's incorporated, add another scoop and repeat once or twice. Pour the cream-egg mixture back into the saucepan with the rest of the cream and return to heat. Continue to whisk constantly until the mixture thickens to a pudding consistency. 

Remove from heat and add cubed butter, stirring to help it melt. Pour through a fine-mesh sieve into another bowl, directly cover the surface with plastic wrap and refrigerate until chilled. Enjoy!