Fold the kale leaves in half lengthwise so that the rib is clearly visible on one side. Cut out the ribs. Stack the kale leaves on top of each other and roll them up lengthwise. Cut them crosswise into very thin (about 1/4-inch) ribbons.
In a large bowl combine the olive oil, lemon juice, Dijon mustard, and salt and pepper to taste. Add the sliced kale and use your fingers to rub the dressing into the kale ribbons. Set aside for up to 30 minutes, or keep going if you don't have extra time.
Cut the romaine crosswise into 1/2-inch slices. Add the sliced romaine to the kale and toss. Add the Grana Padano and toss again. Serve.