Prepare the infused sugar the night before, by adding fresh thyme sprigs and leaves and storing in an airtight container. If you want pieces of the thyme n the batter, blitz the sugar and leaves mixture in a food processor to combine.
Preheat the oven to 325ºF. Grease a Bundt pan and place on a baking sheet.
In the bowl of a stand mixer outfitted with the paddle attachment, mix the butter, sugar and vanilla bean paste until well combined.
Crack the eggs into a bowl and add to the butter mixture one by one, mixing well between each addition so that each is fully incorporated.
Add the pomelo juice and mix to combine. The batter may have a strange appearance, but don’t panic.
Sift together the flour, baking powder and salt in a medium bowl. Run the mixer on low (I use the stir setting on my KA) and alternate adding the flour and milk in three additions. Once all added, increase the mixer to medium-low (setting ¾ on KA) and mix until well combined.
Spoon about 100 grams of the batter into a small bowl and add combine well with the freeze-dried blueberry powder.
Pour half the plain batter into the prepared pan and tap to help it settle into the design of the pan. Spoon in the blueberry batter and use a plastic spatula to swirl it through the batter. Top with remaining batter and bake for 60 minutes. Check for doneness with a toothpick before removing from the oven.
Remove from the oven when ready and allow to cool for 10-15 minutes in the pan on a wire rack. Once cooled, place the wire rack over the open side of the Bundt pan and flip over. Slide the pan off the cake and allow to cool completely.
Make the glaze:
Add the sugar and blueberry powder to a small bowl and whisk together. Spoon in the pomelo juice a bit at a time until it reaches the desired consistency.
Glaze and garnish:
While still on the wire rack, pipe or pour the glaze over the cake. Or you may do this on the serving plate, if you don’t mind the puddles of glaze that form at the base.
Sprinkle with zest and fresh thyme leaves and top with a few randomly placed freeze-dried blueberries.