• Preheat oven to 350°F/175°C and coat a regular-sized donut pan with vegetable spray.
• Prepare the flax egg and set it aside.
• Use a rolling pin to crumble the cookies into a fine crumb, but leaving some texture.
• Add the flour, cookie crumbles ,brown sugar, spice, salt, baking powder, baking soda, and salt in a bowl. Stir to combine.
• Heat vegan butter in a microwave-safe bowl for 20 to 30 seconds, until the butter is melted. Stir in the flax egg, milk, and vinegar.
  
• Pour the milk mixture into the flour mixture.
  
• Stir until just combined. It should be a thick batter without lumps.
  
• Use a tablespoon to carefully distribute the batter into the donut compartments, filling them generously and equally. Use 3 tablespoons of batter per compartment for smaller donuts and 4 tablespoons of batter for thicker donuts. Bake for 12 to 16 minutes, until the donuts are done.
  

For the Glaze

• Heat vegan butter, brown sugar, and cream in a saucepan over medium heat until it comes to a boil. Stir and boil for around 30 seconds.
  
• Remove from heat and allow it to cool for about 5 minutes, then add the powdered sugar and stir to combine. This glaze will thicken as it sits, so be prepared to stir in another tablespoon of cream as needed.

Glazing Donuts

• Once the donuts are done, remove them from the oven and allow them to cool slightly. Once they're cool enough to handle, and the glaze has cooled enough so it won't burn your fingers, dip the top part of each donut in the caramel icing. Optional: Top donuts with biscoff cookies or crumbles.