Set a rack in the lower third of the oven and preheat oven to 350 F. Prepare a Bundt pan by brushing with melted butter and sprinkling with flour, tapping out the excess flour.
Cake Preparation: Sift the flour, Rumford Baking Powder, and salt together. Set aside. Cream the butter and sugar. Add the eggs one at a time, mix thoroughly, stop and scrape as you go to ensure even mixing. Add the flour mixture and chai alternately, beginning and ending with the flour in three parts and the chai in two parts. Mix thoroughly after each addition.
Pour the batter into the prepared pan, smooth the top and bake for about 40 to 45 minutes, until the top springs back when pressed gently with a finger. Allow cooling on a rack for about 20 to 30 minutes, remove cake from pan and continue cooling until complete. Place cake in freezer at this point to aid in glazing.
Glaze Preparation: Sift the powdered sugar with the spices and stir in the chai extract, 1/2 tbsp at a time to form a smooth, thick yet pourable glaze. It should be thick and cling to the cake. Remove cake from freezer and set the cake on a rack over a plate and spoon the glaze in a circular motion. Let it fall in place or smooth with an offset spatula, as you like. After a few minutes, spoon the dripped glaze from the plate back over the cake. Press the crystallized ginger onto the glaze as it sets (if using).