Preheat the oven to 350 F
In a large bowl, combine the coconut sugar, yogurt, cinnamon, oil, eggs and vanilla and whisk together until smooth.
Add in the oat flour, salt, baking soda and baking powder and mix well.
Line a muffin tin with cupcake liners and divide the batter evenly into about 10 liners.
To make the crumb topping, mix together the oat flour, cinnamon and sugar in a small bowl. Add in the cold butter and work the flour mixture into the butter using your hands to break up the butter and form crumbs.
Sprinkle the crumbs over each muffin. Bake for about 18 minutes, until the tops are firm to touch
Let them muffins cool and dust them with powdered sugar. Keep refrigerated for up to 2 weeks, or keep at room temperature for up to 3 days.