To make the bars, melt the butter and white chocolate together in a medium saucepan over medium heat, stirring constantly until smooth, about 7 minutes. Remove from heat and allow to slightly cool for approximately 10 minutes.
While cooling, adjust the oven rack to the lower third position and preheat oven to 350°F. Line the bottom and sides of a 9-inch square baking pan with parchment paper, leaving an overhang on all sides for easy removal once baked. Set aside.
Next, make the chai swir. Mix the swirl ingredients together in a small bowl and set aside.
In a medium bowl, whisk the flour, baking powder, and salt together. Set aside.
Whisk the granulated sugar into the cooled butter and white chocolate mixture. Whisk in the eggs and vanilla. Pour the dry ingredients into the wet ingredients and fold gently until completely incorporated.
Pour half of the batter evenly into the prepared pan. Sprinkle and spread the swirl ingredients evenly on top-- it will be a thick layer of swirl! Cover evenly with remaining batter. See post details for spreading tips.
Bake for 35-40 minutes or until the bars are lightly browned around the sides and on top and a toothpick inserted in the center comes out clean. Cool completely on a wire rack before removing.
Once cooled, make the glaze. Combine all of the ingredients in a medium saucepan over low heat and whisk until smooth. Remove from heat and pour over cooled bars or dip each individual bar into the glaze after cutting into squares. The glaze will set after about 10 minutes.
Store in an air tight container at room temperature for up to one week or store unglazed bars in the freezer for one month. Make the glaze and dip thawed bars in glaze prior to serving.