Preheat oven to 400 degrees. Line muffin pan with paper liners (we prefer PaperChef Lotus Cups for jumbo muffins, as they allow for a large top with no mess). In a medium bowl, combine flour, baking powder and soda, salt and cinnamon; set aside. In mixing bowl on medium speed, beat avocado and butter until combined. Add sugars and beat until blended well; add vanilla and egg and beat smooth, approx.1 min on medium-high speed. Add yogurt and milk and mix until just combined. On medium speed, add half of dry ingredients. When combined, add remainder and mix completely, scraping down sides of bowl periodically. Fold in blueberries by hand and allow batter to rest at room temperature 30 min (this allows ingredients to activate and air bubbles to form, making a lighter muffin). Fill muffin cups almost completely full (gluten-free muffins do not rise very much). Sprinkle each with 1 t of topping mixture; bake 10 min at 400 degrees. Reduce temp to 350 degrees and continue baking until muffins are puffed, deep golden brown and toothpick inserted in center muffin comes out clean, approx. 25-30 min. Serve warm or at room temp, with softened butter, if desired.
*Tip: You can substitute avocado for all of the butter, however, the muffins then need to be cooked at a slightly lower temperature of 325 degrees and for 35-40 min (in addition to the initial 10 min at 400 degrees).