Blueberry-Ginger Buckle

Peel one 2" piece ginger (a spoon makes this easy work). Using a Microplane, finely grate ginger into the bowl of a stand mixer, or a large bowl if using a hand mixer. (Try to avoid adding any of the really stringy bits and compost those.) Add ⅔ cup (133 g) granulated sugar. If using a stand mixer, fit with paddle attachment. Beat on low speed until sugar is moist and fragrant and no large clumps remain. Add remaining 4 Tbsp. unsalted butter, room temperature, increase speed to medium-high, and beat, scraping down sides of bowl 2–3 times, until very pale and fluffy, about 5 minutes.