Preheat the oven to 180°C (gas mark 4, 350°F) and grease a doughnut tray with melted butter.
Add an egg, milk, vanilla, Biscoff and melted butter into a large mixing bowl and mix until combined.
Pour flour, salt, sugar, baking powder and bicarbonate of soda to the mixing bowl and mix together until a batter has formed.
Add crushed Biscoff biscuits to the batter and mix until evenly distributed.
Spoon or pipe the Biscoff donut mixture into the doughnut tray and bake for 8 to 10 minutes.Stick a skewer inside if it comes out clean then it’s ready.
Leave the donuts to cool down for a few minutes before transferring to a cooling rack to cool down completely.
To decorate the donuts, pour the remaining Biscoff spread into a mixing bowl and melt it in the microwave.
Once the donuts have cooled down completely.Dunk each donut into the melted Biscoff and place on a cooling rack glaze side up. Drizzle melted white chocolate and sprinkle crushed Biscoff biscuits. Leave the glaze to harden and enjoy!