Preheat the oven to 350°F (180°C). Prepare two donut trays by spraying them with non-stick spray.
Sift all purpose flour into a mixing bowl and add white granulated sugar, baking powder and salt. Mix together.
Add milk, egg, vanilla extract, melted butter and melted biscoff cookie butter and mix into a batter. Don't overmix.
Place the donut batter into a piping bag and pipe it into the donut partitions evenly.
Bake for 15 minutes until lightly browned on top.
Remove from the oven and let the donuts cool in the pans for a few minutes before transferring them to a wire cooling rack to cool completely.
When the donuts are completely cool, melt the biscoff cookie butter for the topping.
Dip each donut in the melted biscoff cookie butter and then place them onto a parchment lined baking sheet.
When all the donuts have been dipped in the melted biscoff, drizzle melted white chocolate over the top of the donuts.
Place the donuts into the fridge for 10 minutes for the topping to set and then serve.