Preheat the oven to 350°F (175C/155C Fan) and prepare donut trays.
In a large bowl, beat together the butter and sugars.
Next, add the eggs, maple syrup and vanilla, whisking together to incorporate.
Add in the ripe banana. Break this into pieces and blend into the batter.
Add the remaining dry ingredients - the flour, baking soda and salt, beating until just combined.
Slowly add the buttermilk, mixing until just combined to form the batter.
Lastly add in the bacon bits and fold to distribute.
Pipe the batter into 12 prepared donut moulds and bake in a preheated oven for about 20 minutes, checking for the donuts to be risen and lightly golden. You can also test with a toothpick - inserted in one of the middle donuts. Once this comes out clean, your donuts are done.
Remove from the oven. If using silicone trays, allow the donuts to cool for about 5 to 10 minutes before unmoulding carefully. Place on a wire rack to cool completely.