1. 1. Prepare the Custard Mixture: In a shallow dish or pie plate, whisk together the sourdough discard, milk, eggs, granulated sugar, vanilla extract, cinnamon, and salt until well combined and smooth. Ensure there are no lumps of sourdough discard remaining. The mixture should look like a pale, creamy batter.

2. 2. Soak the Bread Slices: Dip each slice of day-old bread into the sourdough custard mixture, allowing it to soak for about 20-30 seconds per side. The bread should be fully coated and absorb some of the liquid, but not become completely soggy. You want it moist, not falling apart.

3. 3. Heat the Skillet: Place a large non-stick skillet or griddle over medium heat. Add about 1 tablespoon of unsalted butter and let it melt, swirling to coat the bottom of the pan. You want the butter to be shimmering, not smoking.

4. 4. Cook the French Toast: Carefully place 2-3 soaked bread slices into the hot skillet, ensuring they aren’t overcrowded. Cook for 3-4 minutes per side, or until golden brown and cooked through. The edges should be slightly crispy, and the center should feel set.

5. 5. Add More Butter (If Needed): As you cook subsequent batches, add another tablespoon of butter to the skillet to prevent sticking and ensure even browning.

6. 6. Keep Warm (Optional): If you’re cooking for a crowd, you can keep the finished French toast warm by placing it on a baking sheet in a preheated oven at 200 F (95 C) while you finish cooking the remaining slices.

7. 7. Serve Immediately: Transfer the cooked French toast to plates. Dust with powdered sugar, drizzle generously with maple syrup, and top with fresh berries, if desired.