Rinse the rhubarb, trim the ends (the leaves are toxic), slice it into 1-inch pieces, and put in a heavy-bottomed pot along with the sugar.

Add 2 tablespoons of water and a squeeze of fresh lemon, and stir to combine.

Heat, stirring constantly, until the rhubarb starts to give off juice and the mixture comes to a boil.

Boil gently for about 15-20 minutes until the rhubarb is soft and mostly broken down.

Puree the mixture in a blender or food processor until as smooth as possible, being cautious with hot foods to avoid splatter.

Put the puree back on the stove and bring to a boil, then turn down the heat and let it gently bubble until reduced and thickened for about another 20 minutes.

Stir often, and watch for scorching. The rhubarb butter is done when it darkens and gets glossy and a spoon can drag across the bottom of the pan without filling in.

Spoon the finished butter into a glass jar, let it cool, cap and refrigerate. You will have about one and a half cups of rhubarb butter.