For the cake: Preheat oven to 350 degrees. Grease Bundt or tube cake pan with 1 Tbsp. butter and dust with 2 Tbsp. flour. Tap out any excess flour. In a medium bowl, sift together flour, Mt. Baker Chai, baking powder and salt. Using a stand mixer, cream together 1 cup butter with sugar until smooth. Mix in one egg at a time to combine then add buttermilk if using. At low speed, slowly add flour mixture to batter until incorporated. Pour batter into prepared pan; tap pan on counter a few times to release any air pockets. Bake for 1 hour or until cake tester comes out clean. Cool cake in pan for 20 to 25 min. Turn cake out onto to a plate or platter before cutting and serving.
For the glaze: Whisk all ingredients together until smooth. Drizzle over slightly warm cake or lightly spread over completely cooled cake.