How to Adjust a Muffin Recipe for Jumbo Size Muffins: 11 Steps (oven 25 degrees lower, bake for 5 additional minutes)
Homemade JUMBO Blueberry Crumb Muffins beat the bakery ones black and blue.
Adjust a Muffin Recipe for Jumbo Size Muffins - wikiHow
made doubled the recipe to yield 24 muffins. Doubling the crumb topping was too much; single recipe sufficient for a double recipe. Used fresh blueberries, and added the zest of one lemon.