Add remaining wet ingredients and whisk well. Add the sifted dry ingredients and mix. Note: No need to sift for gluten-free version.
In small bowl, combine all ingredients except for vegan butter. Mix well. Add vegan butter and rub with fingers until the mixture is crumbly. Keep in refrigerator until needed.
Divide batter between the 6 muffin cups. Sprinkle chilled crumble on top. Make sure crumbles are higher than the edges.