1) To make the crust: Whisk together the flour, Hi-maize, cheese powder, salt, dry mustard, and pepper or hot sauce.
2) Cut the butter into pats, and work it into the flour till the mixture is crumbly.
3) Toss in the cheese. Add the water, tossing with the flour mixture till moistened; add an extra tablespoon or two of water if necessary, to bring the dough together.
4) Divide the dough into four pieces. Pat each into a disk, wrap, and refrigerate for 30 minutes.
5) Transfer the disks to a lightly floured surface, and roll them into 1/8"-thick circles.
6) Place the circles in 4 1/2" tart pans. Prick bottoms with a fork, and chill in the freezer for 15 minutes, while you preheat the oven to 400°F.
7) Bake the tart shells for 12 to 15 minutes, until light brown around the edges. Remove from the oven and cool.
8) To make the filling: Sauté the onion in the 2 tablespoons butter till translucent.
9) Stir in the vinegar and salt. Remove from the heat.
10) Whisk together the eggs, milk, and seasonings.
11) To assemble the tarts: Place 1/4 of the goat cheese into each tart shell. Add 1/4 of the milk-egg mixture, then top with 1/4 of the sautéed onions.
12) Bake the tarts for 18 to 22 minutes. Remove them from the oven, and cool for 10 minutes before removing from the pans. Serve warm, or at room temperature.
Yield: 4 individual tarts.