Preheat oven to 350°F (180°C).
In a bowl, whisk together flour, baking powder, baking soda, salt and nutmeg; set aside.
In a large bowl, whisk together kefir, eggs, butter and vanilla. Add sugar and whisk until combined. Add flour mixture and stir until batter is smooth and no flour remains.
Spoon batter into buttered donut pans and bake for about 10 minutes or until tester inserted in centre comes out clean. Let cool completely.
Glaze: In a bowl, sift icing sugar into a bowl and whisk in charcoal. Whisk in kefir until smooth and runny.
Dip each donut into glaze and place on cooling rack set over a baking sheet. Repeat with remaining donuts.
Sprinkle each donut with edible glitter and swirl; let stand 2 hours to set or enjoy right away!
Tip: To easily fill the donut pans, scrape batter into a resealable bag and cut 1 corner. Squeeze into each donut space equally.