First, cook the sweet potato. You can boil, roast, or microwave the sweet potato until tender. See notes for instructions for each cooking method.
Preheat the oven to 350 degrees F. Grease a 9x9 baking dish and set aside.
Add 1 cup of cooked sweet potato to a mixing bowl, and mash with a fork. Stir in the peanut butter, maple syrup, and vanilla extract until smooth. Add the cocoa powder, and mix well.
Spread the batter into an even layer in the greased baking dish. Top with mini chocolate chips and flaky sea salt (optional). Bake for 35 to 40 minutes. Let the brownies sit for 15 minutes before slicing into pieces.
How to cook sweet potato
Boil: Peel the sweet potato, cut into 1-inch chunks, place in a pot of salted water, bring to a boil, and cook for 15-20 minutes until tender.
Microwave: Poke several holes in the sweet potato skin to let air escape, place on a plate, microwave for 2.5 minutes, turn the potato over, and microwave for another 2.5 minutes.
Roast: Preheat an oven to 400 degrees F, poke several holes in the sweet potato skin, place on a piece of foil or a baking sheet on the center rack of the oven. Cook for 45-60 minutes until tender.
Peanut butter tip: If you have trouble getting peanut butter out of measuring cups, try rinsing the cup in hot water for a few seconds before adding the peanut butter. This will help it glide right out!
Storage: Place in an airtight container, using wax or parchment paper as needed to separate layers of brownies. Store on the counter or in the fridge for up to 5 days.
Freezing: Let the brownies cool completely. Wrap each one in plastic wrap before placing in a freezer-safe bag or container. Freeze for up to 3 months.