Combine butter and canola oil in a large bowl. Stir well.
Stir in sugar.
Add egg, egg white, and vanilla extract. Stir very well, until all ingredients are thoroughly combined.
Add buttermilk and stir well.
In a separate bowl, whisk together flour, baking powder, corn starch, and salt.
Fold dry ingredients into wet gently, taking care not to overmix. Once about half of the dry ingredients have been incorporated into the batter, add in chocolate chips and continue to fold in to batter until all ingredients are just combined.
Cover bowl with a dry towel and allow batter to sit 15 minutes**
Preheat oven to 425F (218C) and line muffin tin with paper liners.
Once oven has preheated, portion batter into 6-cavity large muffin tin (you may also use regular, 12 count muffin tin, you will just need to bake them for less time), filling each tin all the way to the top with batter (without overflowing).
Sprinkle tops generously with sugar and place muffin tin in preheated oven.
Bake on 425F (218C) for 8 minutes and then reduce the oven temperature to 350 (177C) (do not open the oven door or remove the muffins, just leave them in and reduce the temperature) and bake another 15 minutes, or until tops are just beginning to turn golden brown (if you are using a 12-count muffin tin rather than jumbo-sized, these will not need to bake as long. Start checking your muffins after 7-8 minutes on 350F (177C).
Allow to cool, and enjoy!
*If you don't happen to have buttermilk, you can use this substitute: pour 1 1/2 teaspoons lemon juice or vinegar into a measuring cup and then fill up to the 1/2 cup line with regular milk. Stir well and allow mixture to sit for at least 5 minutes (it will thicken) before using.**This is optional, it helps give the muffin tops a higher rise but you can certainly put them straight in the oven without waiting and they'll still taste delicious. Ideally you would let the batter set at least one hour, but I found 15 minutes gives me a decent rise (the muffins in the photographs were allowed 15 minutes) while still not dragging out the process too much. Special thanks to The Kitchen Whisperer for the great tips that helped make these muffins truly "bakery style"!