Preheat your skillet or griddle over medium heat.
If you plan to keep finished slices warm, preheat the oven to 90–95 °C (200 °F) and place a baking sheet inside.
In a large shallow bowl, whisk together the eggs, milk, vanilla, ground cinnamon and a pinch of sea salt until evenly combined and slightly frothy.
Working 2–3 slices at a time, lay each slice of brioche into the custard. Let it soak 5–10 seconds per side for thin/thirsty bread, or 10–20 seconds per side for extra-thick brioche. Don’t let it sit so long that it falls apart you want the center moistened but not dripping.
Add 1 tbsp butter (or coconut oil) to the preheated pan. When it sizzles, place the soaked slices into the skillet (don’t overcrowd).
Cook 2–3 minutes on the first side until deep golden brown, then flip and cook another 2–3 minutes on the second side. Adjust heat as needed — medium-low keeps the inside cooked without burning the outside.
Repeat with remaining slices, adding more butter between batches.
Transfer finished slices to the warm oven-lined baking sheet to hold while you finish the rest.
Stack 2 slices per plate (or 4 if you prefer). Top with strawberries and raspberries, drizzle with maple syrup, and finish with powdered sugar or a dollop of whipped cream if desired. Serve immediately. Enjoy!