Preheat oven to 350°F. When oven is hot, add butter to 9-inch square baking pan and place pan in oven to melt butter. Remove pan from oven and stir in cranberry sauce; return pan to oven until mixture is bubbly, 4 to 6 minutes. Remove from oven; arrange pear slices evenly over sauce; set aside.

Prepare gingerbread mix as directed, substituting reserved pear juice for water. (If necessary, add water to reserved juice in order to equal the amount of liquid called for.) Pour gingerbread batter evenly into pan, being careful not to disturb the layer of pears. Bake for 35 to 38 minutes or until toothpick inserted in center of gingerbread comes out clean. Cool 5 minutes on wire rack; turn out onto serving plate to cool completely.