Preheat the oven to 425°F degrees. In a large bowl, whisk together the flour, sugar, baking powder, and salt.

In a separate bowl, whisk together the buttermilk, egg, melted butter, and vanilla extract. Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.

Transfer the batter to a piping bag or a large Ziploc bag with the corner snipped off. Pipe the batter into a greased donut pan, filling each cavity about halfway full.

Bake for 7 minutes. Remove from the oven and let the donuts cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.

While the donuts are cooling, melt the butter in a small saucepan over low heat. Add the brown sugar and stir constantly for 2 minutes.

Stir in the milk and bring the mixture to a boil. Let it boil for 2 minutes.

Remove the saucepan from the heat and stir in the salt, vanilla extract, and powdered sugar until smooth and well combined.

Dip the tops of the cooled donuts into the glaze. Immediately sprinkle with your desired toppings, such as chopped almonds or granola.