Preheat the oven to 375°F (for high-altitude) or 350°F (for sea-level). Grease a donut pan or cupcake tin. In a small bowl, combine the flour, baking powder, baking soda, cardamom, cinnamon, nutmeg, and salt. Set aside.

In a medium bowl, whisk together the brown sugar, sugar, buttermilk, canola oil, vanilla, and egg until smooth. Add the shredded carrots and chopped nuts until combined. Then, stir the flour mixture into the wet ingredients until just combined.

Spoon the batter into a large piping bag (or a plastic bag with the tip cut off). Pipe the batter into the donut pan cavities about 1/2 way full (don’t go more than halfway, or the batter will rise too much and you won’t get a hole in the center). Bake for about 8-9 minutes, until a toothpick comes out clean.

Let the donuts cool in the pan for about 10 minutes, and then let them cool completely on a rack.

Melt the butter in a small saucepan over medium-low heat. The butter will get foamy and bubbly. Cook for 5-7 minutes, until the butter starts to turn golden and smell nutty. Stir or swirl the pan frequently to prevent the butter from burning. Keep a close eye, because the butter will brown very quickly!

After about 5-7 minutes, you should see some brown bits resting on the bottom of the pan and the butter will smell caramelized. Immediately pour the butter in a medium-sized heat-proof bowl to prevent the butter from burning.

Add the powdered sugar, salt, cardamom, and milk or cream. Stir until smooth, adding more milk or cream 1 Tablespoon at a time until the glaze is the consistency of honey.

Dip each cooled donut halfway into the glaze, letting the excess glaze drip off. Decorate as desired, and let the glaze set completely, about 20 minutes. Store extras in an air-tight container for up to three days.