Rhubarb stars in this homemade and boldly flavored curry ketchup. Make a big batch in the spring to use on burgers all summer long!
Heat oil in a large pot over medium heat. Add onion and cook until soft and beginning to brown, 4 to 6 minutes. Add garlic and cook, stirring, for 1 minute. Add tomato paste, curry powder, salt, paprika, allspice and crushed red pepper; cook, stirring occasionally, for 1 minute. Stir in rhubarb, tomatoes, brown sugar and vinegar. Bring to a boil. Reduce heat to a simmer and cook, stirring occasionally, until the rhubarb is very soft and the sauce is thick, 45 to 55 minutes. Remove from heat.
Puree using an immersion blender or transfer to a regular blender and puree (use caution when pureeing hot liquids).