Makes about 2 cups
8 ounces fresh rhubarb, leaves removed and discarded
2/3 cup sugar
4 large eggs
4 ounces (8 tablespoons) butter, cut into small chunks
Chop rhubarb into 1-inch pieces and place in a small saucepan with enough water to cover. Bring to a boil, then simmer for about 20 minutes until rhubarb is soft and you have a nice pink juice. Strain and let cool. Measure out 2/3 cup of juice for the curd. (Use the leftover pulp in yogurt or dry it into fruit leather. If you have any leftover juice, pour it into a drink!)
Whisk together 2/3 cup rhubarb juice, sugar, and eggs in a small saucepan. Cook over low-medium heat, stirring constantly and scraping the sides and bottom of the pot with a wooden spoon, until the internal temperature reaches 170°F. (If you don't have a thermometer, just watch for it to thicken and coat the back of the spoon.)
Remove from heat and stir in butter. Strain through a fine mesh strainer and let cool.
Cover and refrigerate at least an hour until firm.
You can add spices while the rhubarb is simmering to make the juice, and then strain these out along with the pulp. For example:
• Rhubarb-Vanilla Curd: 1/2 vanilla bean, scraped
• Rhubarb-Ginger Curd: 1-inch knob of ginger, peeled and sliced
• Rhubarb-Cardamom Curd: 2 cardamom pods, lightly crushed