In a shallow wide bowl, whisk together the milk, cornstarch, ground flaxseeds, baking powder, and vanilla. Add butter to a pan over medium-high heat and melt. Whisk the batter again right before dipping bread, as the cornstarch will settle to the bottom of the bowl.
Dip each side of the bread in the batter and let soak for about 10 seconds, then add the bread to the pan and cook for 2-3 minutes on each side, until golden brown. Add more butter to the pan as needed in between pieces of bread. Serve with Nutella and fresh fruit.