In a large mixing bowl, whisk together the flour, cornstarch, sugar, baking powder, baking soda, and salt. Make a well in the center and set aside.
In a microwave-safe bowl, melt the butter, then add the egg, vanilla extract, and buttermilk and whisk to combine. Pour the wet ingredients into the well in the switch to a rubber spatula to gently fold the ingredients together until no flour remains visible. Do NOT overmix! The batter will be lumpy, but this is okay.
Heat the griddle or nonstick pan to medium-low heat and allow it to get all the way hot. Do not grease the pan. Ladle ¼-cup of batter in the center of the pan and allow for it to sit undisturbed until the edges firm up and small bubbles appear on the surface. Add 5-6 more chocolate chips, if desired.
Flip the pancakes and continue cooking until golden brown, 1-2 minutes more. Remove from heat and serve immediately with a drizzle of maple syrup and pat of butter.