Chai milk:
- In a saucepan, bring the milk to a near boil.
- Remove from heat and place the teabags in the hot milk. Allow to steep for 15 minutes.
Boiled milk mixture for frosting:
- Combine the sugar and flour in a saucepan and, whisking continuously, add one cup of the chai milk.
- Cook over medium heat, stirring regularly, until the mixture reaches a pudding-like consistency (about 10 minutes).
- Remove the mixture from the heat and stir in the vanilla.
- Transfer to a bowl, cover with plastic wrap and place in the refrigerator to cool to approximately room temperature.
Chai cake:
- In the bowl of a stand mixer, beat the butter and sugar until light and fluffy (1-2 minutes).
- Add the eggs one at a time, beating on low until just combined.
- Combine the dry ingredients in one bowl (flour, baking powder, salt, cinnamon, ginger, cardamom, allspice and pepper) and the wet ingredients (vanilla, sour cream, milk) in another.
- With the mixer on low, add the dry ingredients in two parts, alternating with the wet ingredients in one (dry, wet, dry). Beat until just combined.
- Evenly divide the batter between three greased, parchment paper-lined 6" round cake pans.
- Bake at 350F for 25-35 minutes, or until a toothpick inserted in the center comes out with only baked crumbs.
- Once the pans are cool enough to handle, turn the cakes out, wrap them in plastic wrap and refrigerate them until cold.
Boiled milk frosting:
- Using the whisk attachment, whip the butter on high until light and fluffy (3-5 minutes).
- Reduce the mixer to low-medium and slowly add the cooled boiled milk mixture one tablespoon at a time, occasionally scraping down the sides.
- Increase the mixer to high and whip until smooth and airy.
Assembly:
- Level the layers of cake (if necessary). Place the first layer on a flat plate and cover with ¼" of frosting.
- Top with the second layer of cake and repeat.
- Top with the final layer, spread a thin layer of frosting over the entire cake and refrigerate until set (about 15 minutes).
- Frost the top and sides of the cake with the remaining frosting and top with fruit, nuts and/or cake-safe flowers.