Heat 4 cups of milk with the tea (either in bags or in a tea strainer) in a large saucepan over medium heat until steaming, about 5-7 minutes. Do not let simmer or boil.

Whisk the sugar, cornstarch and ½ teaspoon salt in a medium mixing bowl. Whisk in the egg yolks and the remaining ½ cup milk.

Whisk half of the hot milk into the egg mixture until smooth, then gradually whisk the egg-milk mixture into the saucepan using a mesh strainer to catch any clumps of egg. Cook over medium heat, whisking constantly, until the mixture begins to bubble. Continue to cook, whisking constantly, until it has thickened to a pudding-like consistency, about 5-6 minutes. Remove from the heat and stir in the vanilla.

Cool slightly, stirring to prevent a skin from forming. Place a piece of plastic wrap directly on top of the custard and refrigerate until completely cooled and thickened, about 4 hours.

Whisk the custard vigorously until smooth and creamy when ready to build trifle.

Preheat oven to 350 degrees F (177 degrees C) and prepare a 9"x13" baking dish by lining with parchment paper. Set aside.

In the bowl of a stand mixer (or in a large bowl using an electric mixer) cream together the butter, vegetable oil, and sugar on medium speed until creamy, light colored, and well combined.

Add eggs, one at a time, incorporating well after each addition.

Mix in vanilla extract.

In a separate medium sized bowl, whisk together flour, baking powder, kosher salt, and chai spices.

Using a spatula and gently hand mixing, alternate adding flour mixture and buttermilk to the butter mixture, mixing until just combined after each addition. The batter should be smooth and completely combined, but avoid over mixing or you will have a dense cake.

Pour batter into your prepared baking dish, and bake at 350 degrees F for 45-55 minutes. When the cake is done, a toothpick inserted in the center should come out mostly clean with few moist crumbs but no wet batter.

Let cool for 15 minutes in pan, then turn out onto a wire cooling rack for one hour before cutting into cubes for trifle.

With a stand mixer or hand mixer and a large mixing bowl, pour in heavy cream and whip on medium speed. When the cream starts to thicken, about a minute in, stop and add the powdered sugar and vanilla extract. Whip for another 2-3 minutes until the whipped cream is thickened and stiff. Do not over whip, you'll make butter.

In trifle bowls, layer cubes of cake on the bottom, add custard, then spoon a layer of whipped cream. Repeat cake, custard, whipped cream, cake, etc, until trifle bowls are filled with whipped cream being the last layer.

Serve with a sprinkle of cinnamon on top.