Heat the oven to 400°F (204°C) with a rack positioned in the middle. The center position gives the bread room to brown without sitting too close to the upper heating element.

Cover a sheet pan with parchment, arrange the bread on it, and compress each center with the back of a spoon or the flat bottom of a ramekin. Leave roughly a ½-inch border and an intact bread base so each slice forms a shallow cup without holes.

Combine the yogurt, egg, honey or maple syrup if using, cinnamon, and nutmeg in a medium bowl, then whisk thoroughly. The mixture should look evenly colored and smooth, with no visible streaks of egg white.

Spoon about 2 tablespoons of filling into each bread well, adjusting to the size of the slice. Stop below the surrounding border rather than forcing extra custard into a well that cannot hold it.

Distribute the raspberries, blackberries, blueberries, and sliced strawberries across the filled centers, adding another drizzle of honey if desired. Keep the fruit within the wells so the exposed bread edges can crisp.

Bake for 12 to 14 minutes, checking for golden bread and a set custard center. A gentle nudge of the pan should produce a small, cohesive tremble in the filling rather than a liquid ripple, with softened berries around it.

Leave the toast on the sheet pan for 5 minutes before lifting it, then dust with powdered sugar if desired. The brief rest helps the filling firm enough to move while the toast remains warm.