For the salad: Place the salad greens in a large bowl. Mix in the cranberries, walnuts, mandarin oranges, grape tomatoes and feta.
For the vinaigrette: Combine the raspberries, vinegars, sugar and mustard in a blender until smooth. Slowly stream in the oil until combined.
Toss the salad with the vinaigrette before serving.
Aged balsamic vinegar gives this vinaigrette a bold, rich flavor. Increase the sugar if your raspberries aren't sweet enough for your taste.