Grilled jumbo shrimp paired with tiny green beans and drizzled with a brilliant red beet vinaigrette is as pleasing to the eye as it is to the palate. Each component of this composed salad can be made in advance. Be sure to roast the beets to capture their sweet intensity (which would be lost if they were boiled). If you have a squeeze bottle with a narrow tip, transfer the vinaigrette to this container so you can artistically drizzle the beet dressing on your plates for a professional presentation. The beet vinaigrette is also delicious served with leafy greens or grilled fish.
Place the shrimp in a medium-size bowl and toss with the sherry, olive oil, tarragon, and lemon juice. Cover the bowl and refrigerate the shrimp for 1 hour.
Position a rack in the middle of the oven and preheat the oven to 400 degrees F. Scrub the beet to remove dirt, then wrap the beet in aluminum foil. Place the beet on a small tray and roast until very tender when pierced with a skewer or the tip of a knife, 60 to 70 minutes. Remove from the oven and let the beet cool in its foil wrapper. When cool enough to handle, peel and cut the beet into 1-inch cubes. Place the beet in a blender or small food processor, and add the oil and sherry vinegar. Purée until the mixture is smooth, then season to taste with salt and pepper. Strain the mixture through a fine mesh sieve and set the vinaigrette aside at room temperature. If you're making the dressing more than a few hours in advance, refrigerate in a covered container for up to 3 days.
Cut the beans so they're all the same length for an attractive presentation. Bring a medium-size pan of water to a boil over high heat. Add 1 tablespoon of salt to the water and blanch the beans for 1 minute. Drain immediately and refresh the beans under cold running water, or plunge them into a bowl of ice water to stop the cooking process. Drain again and set the beans aside to dry on a clean kitchen towel.
To assemble the salad, remove the shrimp from the marinade. Grill on a very hot barbecue until cooked through, turning once, 2 to 3 minutes per side. Be careful not to overcook the shrimp, or they'll be dry and tough. Remove the shrimp with tongs and set aside.
Place the walnut oil, sesame oil, and sherry vinegar in a medium-size pan and warm over medium heat. Add the green beans, stir to coat, and cook until they are warm 1 to 2 minutes. Season with salt and pepper, then divide the warm beans among 4 large plates, piling them in a mound in the center of each plate. Sprinkle the beans with chopped tarragon and toasted sesame seeds. Arrange 4 grilled shrimp on each plate. Generously drizzle the beet vinaigrette around the edges of the plates and serve.