In a small bowl, whisk together the vinegar, salt, pepper, and mustard. Drizzle in the olive oil, whisking constantly until the dressing is completely emulsified. Assemble all the ingredients for the salad on the counter top just before you are ready to serve it. Turn a gas or electric burner to medium high heat. Using an oven glove to protect your hands, heat a large stainless bowl until it is very hot. Add just under 1/2 cup of the vinaigrette, reserving the rest for another use. Swirl for a minute or two, until the vinaigrette is quite warm. Remove from the heat and quickly throw in the spinach leaves and the shallots. Immediately start tossing the salad mixture with tongs and, as soon as it begins to wilt, serve the salad, sprinkled with the toasted pipettes and, if desired, the cheese.
Bring a large saucepan of water to the boil and blanch the shallots for 1 minute. Drain in a colander. When the shallots are cool enough to handle, peel them. In a medium saucepan, combine the vinegar, wine, sugar, mustard seeds, peppercorns, chile flakes, and salt. Stir over low heat until the sugar has dissolved. Add the shallots and bring the liquid to a boil. Simmer for 5 minutes, then remove from the heat and let cool completely. Transfer the shallots and all the liquid into a sterilized jar, cover tightly, and use as directed in this recipe, or keep for up to 2 weeks.
To toast pepitas, preheat the oven to 375 degrees. Toss the pepitas in a bowl with salt, pepper, and cumin to taste. Spread the mixture on a baking sheet and bake for about 5 minutes, shaking once or twice, until lightly browned.
c.1997, M.S. Milliken & S. Feniger, all rights reserved