Whisk eggs, milk, sugar, vanilla, cinnamon, and salt in a wide shallow dish until completely smooth.
Preheat a large skillet over medium heat for 1–2 minutes.
Dip each bread slice in the custard for about 15 seconds per side — just enough to coat, not soak.
Melt 1 tablespoon butter (plus a little oil if using) in the skillet. Add 2–3 slices without crowding.
Cook 2–3 minutes per side until deep golden brown and crisp at the edges.
Transfer cooked slices to a wire rack (not a stacked plate) while finishing remaining batches, adding more butter as needed.
Optional: for extra-thick slices, finish in a 375°F oven for 5 minutes.
Serve immediately with maple syrup, powdered sugar, and fresh berries.