Combine raisins and bourbon in a bowl; let stand 1 hour.
Cut tenderloins lengthwise down center, cutting to but not through bottom. Alternate apple and onion slices down center of each tenderloin. Top slices evenly with raisins, garlic, and rosemary.
Close tenderloins over filling, and tie at 1-inch intervals. Place on sheets of heavy-duty aluminum foil.
Stir together syrup, sugar, and mustard; brush half of mixture over tenderloins. Close foil, and fold to seal. Place in a 13- x 9-inch pan.
Bake at 325° for 25 minutes. Open foil, and brush with remaining syrup mixture. Close foil, and bake 20 to 25 more minutes or until a meat thermometer inserted in thickest portion reaches 160°.
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