Preheat your oven to 325°F and line a large baking sheet with parchment paper.
Add the brown sugar, cinnamon, vanilla, oil, and water to a bowl, then whisk to combine until the sugar is dissolved. Add the raw shelled peanuts to the bowl and stir well to coat the peanuts completely. Pour the peanuts onto the parchment-lined baking sheet and spread into a single layer, pouring any extra liquid in the bowl over the peanuts. (See notes regarding glaze)
Place the baking sheet onto the center rack of your preheated oven and roast for 10 minutes. Carefully remove from the oven, stir, then return to the oven for an additional 5 – 10 minutes. Check the peanuts after 5 minutes to make sure they do not burn, since peanuts and ovens can vary. (I roast mine for a full 20 minutes, but yours may be ready sooner.)
Once the peanuts are cooked to your liking, carefully remove them from the oven, stir well, and separate the peanuts so they do not stick together. Sprinkle the peanuts with a pinch of salt if desired.
Allow the peanuts to cool completely on the baking sheet for at least 10 - 15 minutes or more.