Preheat your oven to 400 °F and spray a muffin tray with non-stick cooking spray. Set aside.
In a small bowl, prepare your flax egg by whisking 1 tablespoon of ground flaxseed with three tablespoons of water. Set aside to gel while you prepare the rest of the batter.
In a large bowl, whisk together the dry ingredients: flour, sugar, baking powder, salt, and optional spices if using.
Add in the wet ingredients (including mashed fruit, fruit puree, or shredded ingredients if using) and mix until just combined.
Fold in the dry mix-ins. Evenly divide the batter among the 12 muffin tins and bake for about 20-25 minutes until a toothpick inserted into the middle comes out clean. Watch the muffins carefully towards the end of the baking time to make sure they don't overbake. The time will depend on the ingredients you use!
Allow the muffins to cool slightly before removing them from the pan. Store in an air-tight container outside of the fridge for a couple days or in the fridge for up to a week.
