Preheat oven to 180ᵒC/160ᵒC fan forced. Lightly grease two 12-hole non-stick donut pans with 7cm-diameter rings. Sift flour, baking powder, cinnamon, ginger and nutmeg into a large bowl. Stir in brown sugar. Make a well in the centre.
Combine the apple, milk and butter in a bowl. Add to the dry ingredients and stir well to combine.
Spoon mixture into a piping bag fitted with a 2cm plain nozzle. Pipe into the prepared pans, dividing evenly among them. Smooth the surface with the back of a spoon dipped in water. Bake for 15 minutes or until a skewer inserted in the donuts comes out clean. Set aside in the pans for 2 minutes, then turn onto a wire rack to cool slightly.
Meanwhile, for the topping, combine the sugar and bacon in a large sealable plastic bag.
Working with 1 hot donut at a time, brush lightly with butter and place in bacon-sugar bag. Seal bag and gently shake to completely coat donut. Remove donut, shaking off excess sugar, and return to wire rack. Drizzle donuts with maple syrup and serve warm.