Preheat the oven to 350ºF. Spread out the black beans on a large rimmed baking sheet so that they are in a single layer. Place them in the oven to dry out until they start to split, about 15 minutes.
Meanwhile, heat the olive oil in a skillet over medium high heat. Saute the onion until softened, about 5 minutes, then add in the garlic and stir for one more minute. Remove from the heat.
In a large bowl, combine the sauteed onion and garlic, beans, sweet potato, oat flour (or flax seed), BBQ sauce, cumin and salt. Use a fork to stir the mixture, mashing the beans to help the batter stick together. You don't want to mash all of the beans, as they help add texture, but you want it mashed enough that you can form and shape the burger patties.
Using the same baking sheet from earlier, line it with parchment paper. With a 1/3 cup measure, scoop the black bean mixture and place the mound on the prepared baking sheet. Use your hands to shape it into a burger about 3/4-inch thick. (Wet hands will help prevent sticking, if necessary.) This recipe should make 8 to 9 burgers.
Bake the burgers at 350ºF for 20 minutes, then use a spatula to gently flip them over and bake for another 5 to 10 minutes. The finished burgers will feel a little dry around the edges, but still slightly soft to the touch in the center. As they cool, they will firm up and dry out a bit more, so you don't want to over cook them.
Serve the burgers warm with your favorite buns and toppings. Leftovers can be stored in an airtight container in the fridge for up to a week, or in the freezer for up to 3 months.
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Notes
Nutrition information is for 1 of 8 burger patties. This information is automatically calculated and is just an estimate, not a guarantee.Thanks to Serious Eats for sharing this brilliant bean-drying technique.Update Note: This recipe was updated in April 2024 with new photos, but the original recipe has not changed.