Preheat the griddle/non-stick skillet over medium heat.
Add whole milk, cornstarch/custard powder, sugar, vanilla extract, ground cinnamon, and a pinch of salt (a little less than 1/8th teaspoon) in a shallow bowl. Mix until well combined.
Melt about 1/2 tablespoon of butter in a skillet/cast iron pan over medium heat.
Give the batter a quick mix once again.
Dip the bread into the mixture, just enough to coat both sides. If using thin slices, do not soak too much as it will turn soggy. If using thick slices, make sure the bread is soaked enough to absorb the milk-cornstarch mixture.
Shake off the excess milk mixture and place the soaked bread on the skillet. Cook until it is golden brown on one side, about 1-1/2 to 2 minutes.
Flip the slices using a spatula and cook the other side until it turns golden brown, another 1-1/2 to 2 minutes. Transfer to a serving plate.
Depending on the size of your pan, you may cook 2 to 3 toasts at a time. Prepare the rest of the French toasts in the same way.
Remember to whisk the batter each time before using as cornstarch settles at the bottom.
Serve immediately, drizzled with maple syrup and toppings of your choice.