Fudgy Sweet Potato Brownies

Roast a large sweet potato at 400°F (200°C) for 45 to 60 minutes until very soft. Scoop out and mash or blend until smooth; measure 1 cup.
Heat the oven to 350°F (175°C). Line an 8x8-inch (20 cm) pan with parchment, leaving an overhang on two sides.
Melt the chocolate and butter in the microwave in 20-second bursts, stirring between each, until smooth. Cool 5 minutes.
Whisk in the brown sugar, then the eggs one at a time, then the vanilla. Whisk 1 minute more for a shiny top.
Stir in the mashed sweet potato until no orange streaks remain.
Whisk the flour, cocoa, cinnamon and salt together and fold into the batter until just combined. Fold in the chocolate chips.
Spread in the pan and bake 28 to 34 minutes, until the edges are set and a toothpick in the center comes out with moist crumbs.
Optional: scatter the marshmallows and pecans over the hot brownies and broil 1 to 2 minutes, watching closely, until golden.
Cool at least 2 hours (or 1 hour in the fridge) before cutting into 16 squares.