Step 1Toss onion with white wine vinegar nearly to cover and refrigerate to crisp and color until needed, 20 to 25 minutes.
Step 2Trim beets, leaving 1 inch of stems and tails. Reserve greens. Steam beets until a knife pierces them easily, 15 to 20 minutes. Slip off skins with your hands. Trim tops and tails and quarter beets. Sprinkle with a little red wine vinegar. Steam greens until tender, then refrigerate.
Step 3Toast pine nuts in dry skillet over medium heat until golden, 5 to 10 minutes, then remove to a plate.
Step 4Cover bread with 2 tablespoons red wine vinegar. Pound garlic in mortar with salt until smooth, then add vinegar-soaked bread, marjoram, parsley and half pine nuts. Pound into a fragrant paste. Stir in olive oil to make a thick dressing (add the larger amount if you want more of salsa verde), and season with pepper.
Step 5Toss beets with sauce. Place beets on individual plates or single platter with greens. Remove onion slices from vinegar and strew them over beets. Garnish with remaining pine nuts and serve.