In a medium saucepan, combine 1 cup of granulated sugar and 1 cup of water over medium heat. Stir gently until the sugar completely dissolves into a clear syrup, about 3–5 minutes.

Once the syrup is ready, add 2 cups of chopped rhubarb to the pan. Increase the heat slightly to bring the mixture to a gentle simmer, simmer for about 5 minutes until rhubarb starts softening.

Reduce the heat to low and let it cook for an additional 10–15 minutes. Stir occasionally to prevent sticking, until the rhubarb is tender but holds its shape.

Remove from heat and stir in 1 teaspoon of vanilla extract and ½ teaspoon of ground cinnamon, if using. Let rest for a few minutes.

Let the candied rhubarb cool in the syrup for at least 30 minutes at room temperature.

Carefully transfer the candied rhubarb and its syrup into an airtight jar and store in the refrigerator for up to two weeks.