Make the apple filling. In a small skillet over medium heat, melt 2 tablespoons of butter. Add diced apples, brown sugar, cinnamon, nutmeg, and lemon juice. Cook for 5–7 minutes, stirring, until the apples are soft and glossy but not mushy. Stir in 1/2 teaspoon vanilla. Set aside to cool slightly.

Mix the custard. In a shallow bowl, whisk eggs, milk, remaining 1/2 teaspoon vanilla, a pinch of salt, and maple syrup or sugar if using.

Prep the bread pockets. Use a small knife to cut a slit in the bottom or side of each bread slice, forming a pocket without cutting through. Gently stuff each pocket with a few spoonfuls of the apple mixture. Don’t overfill; you’ll use any extra as a topping.

Heat the pan. Set a nonstick skillet or griddle over medium heat and add a pat of butter. You want a light sizzle, not smoke.

Dip and cook. Dip each stuffed slice in the custard for 3–4 seconds per side. Let the excess drip off. Place on the hot pan and cook for 2–3 minutes per side, until golden brown and set. Adjust the heat as needed so the toast cooks through without burning.

Finish and serve. Top with remaining apples, a dusting of powdered sugar, a sprinkle of cinnamon, or a drizzle of maple syrup. Serve warm.