Thinly slice apples. Heat chopped walnuts in a small nonstick skillet over medium heat, stirring often, 3 to 5 minutes or until toasted and fragrant. Combine cream cheese, blue cheese crumbles, honey, and toasted walnuts until blended. Add freshly ground pepper to taste. Spread 1 side of each of 28 thin bread slices with 1 Tbsp. cream cheese mixture. Divide 1/2 of the arugula among 14 bread slices. Top with apple slices and remaining 14 bread slices, cream cheese mixture sides down. Melt 1 Tbsp. butter on a griddle over medium heat. Cook 7 sandwiches 3 to 4 minutes on each side until golden and cheese is melted. Repeat procedure with 1 Tbsp. butter and remaining sandwiches.
Tip: If you don't have a griddle, omit butter, and cook sandwiches, in batches, in a lightly greased large nonstick skillet 3 to 4 minutes on each side or until golden and cheese is melted.
*For testing purposes only, we used Pepperidge Farm Very Thin White Bread.