Add the oil to a large pot over medium heat until shimmering.
Meanwhile, peel and chop the onion into a medium dice. Mince the garlic cloves. Add both to the hot oil with 1/2 tsp. fine seal salt and saute until soft and translucent, about 8-10 minutes (it's fine if they start to turn golden).
Scoot the onions to the sides of the pan. Add the chili powder, cumin and cinnamon to the center of the pot and saute for 30 seconds until fragrant, stirring constantly (this will "bloom" the spices to draw out their flavor). Stir into the onions, then scoot them again to the sides of the pan.
Scoop the tomato paste onto the center of the pot and saute for 1-2 minutes, until slightly darker in color. Stir into the onions.
Add one pound of ground beef and break it up into smaller and smaller chunks as it browns, flipping them around to brown on all sides, about 8-10 minutes.
Add roughly 1/2 cup of the beef broth and use the liquid to scrape up any brown bits off the bottom of the pot (they add a lot of flavor). Add the rest of the broth, the tomato sauce, the black cocoa and 1 tsp. fine sea salt. Turn the heat up to bring to a boil, then lower heat and simmer for 10 minutes. Stir occasionally, making sure to scrape the bottom of the pot.
Add the second pound of ground beef and break it up as much as you can while stirring it around in the chili. As it cooks it will disintegrate more. Simmer for 10 minutes. Stir occasionally, making sure to scrape the bottom of the pot. If it looks like it's reducing too much and getting too thick, add a bit of water to thin it out.
Meanwhile, peel and dice the sweet potatoes. Stir into the chili and simmer for 10-15 minutes. Once a fork easily slides into a piece, the chili is ready. Taste and add more salt if necessary.
Serve with your favorite toppings!