Split the sweet potato lengthwise and cool it for 15 minutes. Peel it, blend smooth, and weigh out 245 grams.

Lower the oven to 350°F. Grease the 8x8-inch pan and line it with parchment, leaving two sides hanging over. Set the eggs in warm water for 10 minutes and cool the melted butter for 5 minutes.

Whisk the puree, butter, granulated sugar, and brown sugar in a large bowl for 1 minute, until glossy with no gritty sugar showing.

Whisk in the eggs one at a time for 30 seconds each, then the vanilla, until the batter looks lighter and thicker, like pudding.

Sift the flour, cocoa, baking powder, and salt over the bowl. Fold with a spatula for 20 to 25 strokes, until no dry flour shows and the batter looks thick and glossy.

Fold in 1/2 cup of the chocolate chips. Scrape the batter into the pan, spread it into the corners, and scatter the remaining 1/4 cup chips on top, until the surface looks level.

Bake at 350°F for 30 to 35 minutes, turning the pan once at 15 minutes, until the edges pull from the pan, the top looks set and matte, and a toothpick in the center shows a few moist crumbs.

Cool in the pan on a wire rack for 1 hour, until the top feels firm and the center does not jiggle.

Lift the slab out by the parchment and cut it into 16 squares, 4 by 4, until each square shows a glossy, fudgy center.