Melt 1/2 tablespoon butter in a skillet over medium heat. Add apple slices and salt and cook for 3 to 4 minutes, turning gently, until slightly softened but still intact.
Transfer apples to a plate and let excess steam escape for 2 minutes. Wipe the skillet and lower the heat to medium-low.
Divide half the Brie between 2 bread slices, add apple slices and drizzle each with 1/2 teaspoon honey. Add remaining Brie and close the sandwiches.
Spread remaining butter over the outer faces. Cook in the skillet for 4 to 5 minutes per side until the walnut bread is golden and the Brie has softened throughout.
Rest for 1 minute and cut each sandwich in half before serving.