, 70-85%, very finely chopped
Line a 12-cup muffin pan with silicone cupcake liners, then lightly spray with oil.
Pour oats into a food processor. Whirl until very finely ground, about 2 min. Add cocoa, flax meal, baking powder, baking soda and salt. Whirl until combined, about 1 min.
Whisk egg whites with applesauce, yogurt, agave syrup and vanilla in a large bowl until combined. Add to food processor along with hot water. Whirl until combined, about 1 min. Scrape back
into bowl. Batter will be runny. Let batter stand until thickened to the consistency of oatmeal, about 20 min.
Preheat oven to 350F. Stir chopped dark chocolate into thickened batter. Divide batter among prepared muffin cups.
Bake in centre of oven until muffins have risen and a skewer inserted in centre of muffins comes out slightly sticky but not wet, 25 to 27 min. Let muffins cool in pan for 15 min. Transfer to a rack to cool completely. Frost with Vanilla marshmallow frosting. (Prep Tip: Muffins will stick to paper liners; use silicone liners for easy removal. Or spray muffin cups with oil if not using liners.)