1) Beat together the eggs, oil, sugar, vanilla, and salt at medium-high speed until thickened and light-colored, about 5 minutes.
2) Beat in the flour and baking powder.
3) Mix in the chips and nuts. Cover and refrigerate for 3 hours, or overnight.
4) Preheat the oven to 350°F. Lightly grease (or line with parchment) two baking sheets.
5) Divide the dough into four even pieces, about 13 ounces each if you have a scale.
6) Working with one piece at a time, place the dough on the prepared baking sheet, shaping it into an 8" x 2" log. Repeat with the remaining pieces of dough, leaving at least 2" between them; you'll put 2 logs on each baking sheet.
7) Sprinkle the logs heavily with coarse white sugar, if desired.
8) Bake the logs for about 28 to 30 minutes, until they're set and beginning to brown and the edges and sides, but not brown all over. Remove them from the oven, and reduce the oven temperature to 300°F.
9) Spritz the logs lightly with water; this will make them easier to cut. Allow them to cool for 10 minutes.
10) Cut each log into 1/2" to 3/4" slices. Cutting them on the diagonal will make the mandelbrot longer; cutting them crosswise will yield shorter cookies.
11) Place the pieces on edge, quite close together, on the baking sheets, and return them to the oven.
12) Bake for an additional 35 to 45 minutes, until a cookie feels baked through when you pinch it between your fingers. You'll also notice some browning around the edges, though the cookie shouldn't be browning all over. The point is simply to bake them all the way through.
13) Remove from the oven, and cool the mandelbrot right on the baking sheets.