Preheat the oven to fan assisted 160C / 180C / 350F / gas 4 and lightly oil two 6 cup doughnut tins.

Mix together the flour, sugar, baking powder and salt in a large bowl and set aside.

In another bowl, combine the buttermilk, eggs, melted butter, orange juice and orange zest.

Mix the wet ingredients into the dry ingredients and stir until everything is just combined.

Using a spoon, add the batter in to 8 doughnut cups until they are three quarters full.

Bake the doughnuts for 13-15 mins until a toothpick comes out clean, remove them from the oven and let them cool in the pan before transferring them to wire rack to cool completely.

Mix together the sugar and cinnamon in a bowl. Dip the donuts in the melted butter, let the excess butter drip off before dipping in the cinnamon sugar till they are well coated.