For the pate brisee:

In the bowl of an electric mixer, use dough hook on low speed to combine the flour, salt, and sugar. Add the butter by chunks. When the mixture is the consistency of coarse meal, add the water and mix thoroughly, but do not overmixed. The dough will be moist (but it will be tough if overmixed).

Gently shape the dough into a ball, wrap in plastic wrap, and refrigerate at least 4 hours or overnight

When ready to hake, divide the dough into 6 equal pieces. On a lightly floured board, roll each piece 1/8 inch thick and press into a 4-to 4½-inch tart pan, making sure it extends ¾ inch up the sides of the pan. Refrigerate 1 to 2 hours.

Preheat the oven to 400°F. Line each shell with aluminum foil and fill with beans or pie weights. Bake 15 minutes, then remove the foil and beans, reduce the temperature to 375°F., and bake until light golden brown, about 10 minutes.

For the onion confit:

In a large skillet, heat the oil and butter over high heat until shimmering. Add tbe onions, sprinkle with the sugar, and cook without stirring for 5 minutes. Stir, then continue to cook, stirring occasionally, for another 5 minutes. Reduce the heat to medium-high and cook 5 minutes more. Raise the heat to high, add ½ cup of stock, and boil for 1 minute. Add the vinegar and continue cooking 10 to 12 minutes, reducing the heat to medium-high as the onions begin to brown.

Taste and add stock if the onions are too tart, or vinegar if they are too sweet. Season with salt and pepper and keep warm.

To serve:

Remove the shells from the tart pans. Spoon about ½ cup of the onions into each shell, sprinkle with the minced chives, and place on individual serving plates. Drizzle each plate with the optional chive oil.

Variation:

Substitute balsamic vinegar for sherry vinegar, Perfect Flaky Piecrust or frozen purchased puff pastry for the pate brisee.