Preheat your fan oven to 160˚C (325˚F) or 175˚C (350˚F) if you're not using a fan oven. Using a cooking spray or butter, grease large donut pan (6 holes).
In a medium sized bowl, sift together all-purpose flour, baking powder, nutmeg and salt. These are your dry ingredients.In a measuring jug combine together buttermilk and vanilla extract. These are your wet ingredients.
Using a stand/hand mixer, beat together butter and sugar until pale and fluffy. Approx. 1-2 minutes. Add an egg and beat until it's incorporated. Next, dry and wet ingredients alternating between one another. (flour, buttermilk, flour) The batter will be thicker than the cake batter.
Put the batter into a piping bag, snip the end and fill donut pan ¾ of the way full. Bake in a preheated oven for 10-12 minutes.
Once your donuts are baked, leave them in the pan for 2-3 minutes before transferring them to a cooling rack to cool completely.
glaze and toppings
Place finely chopped dark chocolate in a medium sized bowl and pour over it almost boiling heavy cream. Cover it with a plate and leave it for 2-3 minutes. Stir with a silicone spatula to combine.
Dip cooled donuts in chocolate glaze, put them on cooling rack and then top with marshmallows, crushed pretzels and biscoff cookies. I suggest you first put the marshmallows, blowtorch them and then add the rest of the toppings.