Preheat oven to 425℉ and lightly grease muffin cups or line with muffin papers.
Add milk, eggs, vanilla, butter and sugar to the blender pitcher and secure lid.
Blend on “Med” manual setting for 10 seconds. Select “Cancel” to stop blending.
Add dry ingredients to the blender pitcher and secure lid.
Using tamper to aid in blending, select the “Low” manual setting until the mixture is wet, approximately 25 seconds. Select “Cancel” to stop blending.
Using a rubber spatula, fold 1 cup of chocolate chips into the batter. Spoon batter into prepared muffin cups until cups are ⅔ full.
Sprinkle remaining chocolate chips and crystalized sugar, if using, over top of muffin batter.
Bake muffins in oven preheated to 425℉ for 7 minutes then reduce temperature to 375℉ and baking for additional 7-12 minutes until golden brown and a toothpick inserted into center of muffin comes out clean.