Remove the crusts from the sourdough brioche or challah and slice into 1-inch thick sticks. If not stale, preheat oven to 250°F and lay sticks on a baking sheet for 5-10 minutes to dry out.

In a shallow mixing bowl, whisk together the eggs, whole milk, kosher salt, and vanilla until smooth to create the custard.

Blend the granulated sugar with the ground cinnamon on a plate, adjusting the cinnamon to your taste. Set aside for coating.

Heat the butter or coconut oil in a skillet over medium heat. Dip each bread stick into the custard quickly, letting the excess drip off, and cook in the skillet for 2-3 minutes on each side until golden and crispy.

Toss the cooked French toast sticks in the prepared cinnamon sugar while warm.

Keep cooked sticks warm in a preheated oven at 200°F if making multiple batches.