Preheat the oven to 450ºF. Place a rimmed baking sheet in the oven while it preheats.

Using the shredding attachment on a food processor, grate the potatoes and onions and pile the shreds on top of a clean dishtowel. Squeeze out as much liquid as you can, then pour into a large bowl. Mix in eggs, arrowroot, salt, and pepper.

Using oven mitts, remove the hot baking sheet from the oven. Pour the canola oil onto the pan and brush into an even layer with a silicone pastry brush. Return to the oven for 30 seconds.

Remove the sheet from the oven. Using a medium cookie scoop, portion the potato mixture onto the hot, oiled baking sheet. Flatten each mound slightly. (If a lot of liquid begins to accumulate in the bowl, drain the potato mixture again in a sieve.)

Place in the oven and bake for 20 minutes, flipping halfway through. Drain on paper towels to absorb any excess oil. Serve immediately or keep in a warm oven until ready to serve.

Combine all ingredients in a small saucepan. Bring to a boil, then cover, reduce heat to very low, and simmer for 60 minutes. Uncover and simmer for an additional 40 minutes, until thickened. Remove cinnamon sticks and rosemary sprigs before serving.