Preheat oven to 350. Cut ½" strips of unbleached parchment paper and line muffin tins with two strips making an "X". Dab a bit of water on the back of the parchment, if needed, to hold it down.
Place all ingredients of muffin recipe into a blender. Blend well. Stop to scrape down the sides, several times, so all batter is incorporated.
In a small bowl, mix together ingredients for streusel toppings.
Scoop batter into prepared muffin tins. Evenly divide batter into 12 muffins, filled almost to the top.
Spoon streusel topping onto muffins. It will be quite sticky.
Bake for 25-28 minutes, until toothpick comes out clean when inserted.
Let muffins cool in tin for 15 minutes. Gently lift muffins out of tin by gripping ends of parchment. Peel off the parchment paper and allow muffins to continue cooling on wire rack.
Store at room temp for 5 days or in the freezer for up to 3 months.
Notes
Streusel topping can be quite sticky. Either use a spoon or I found that wet hands will help you distribute it more easily.