1. Remove the scallops from the fridge, use a paper towel to dry them very well, and season generously with salt and pepper.
2. Mix the lemon juice, vinegar, shallot, and 1 Tbsp of the olive oil in the bottom of a large bowl.
3. Use a peeler to shave 4 of the asparagus spears and add them to the bowl along with the watercress. Cut the remaining 8 asparagus spears into 1/2-inch pieces and set aside.
4. Heat a large sauté pan over medium-high heat. Add 1 Tbsp of the olive oil, the snap peas, and the asparagus pieces, season with salt and pepper, and sauté for 1-2 minutes, or until just barely cooked. Add to the bowl with the watercress and shaved asparagus.
5. Add the remaining 2 Tbsp olive oil to the sauté pan, then add the scallops, leaving them to sear on one side, undisturbed, until very crispy and almost cooked through, 3-5 minutes. Flip the scallops, then reduce the heat to low and add the butter. The butter will immediately sizzle and start to turn brown. Turn off the heat (the residual heat will finish cooking the scallops).
6. Toss the watercress-asparagus salad to combine well. Divide the salad among four plates (or arrange it on one platter), arrange the cooked scallops on top of the salad, and pour the brown butter over. Garnish with a little coarse sea salt and serve with lemon wedges on the side, if desired.