Preheat an oven to 350 degrees F. Rub 2 tablespoons mustard and beer onto the pork tenderloin and leave at room temperature for 20 minutes. Heat the oil in an oven-proof frying pan until shimmering. Add the pork and sear on all sides until golden, about 6 minutes. Move the pan to the oven. Cook until the internal temperature of the thickest part of the pork is 160 degrees F, about 15-20 minutes. Place the tenderloin on a cutting board and let rest while you prepare the salad.
Make the dressing by combining the remaining mustard, olive oil and balsamic vinegar in a large salad bowl. Season to taste with salt and pepper. Add the greens and half of the raisins to the bowl and toss with the dressing. Divide the salad amongst four dinner plates. Slice the tenderloin into thin rounds, and place equal portions on each of the salads. Sprinkle with more raisins, and serve immediately.
