In a food processor, pulse the chopped rhubarb until as finely chopped as possible. Strain the rhubarb pulp though a fine sieve into a bowl, help with a wooden spoon to press as much juice as possible. Measure out 1 cup juice and pour it into a large bowl, reserve the rest.
Add eggs, corn flour and sugar into the bowl with 1 cup rhubarb juice, mix until well combined. Add diced butter, then transfer the mixture into a pot and place over low heat. Cook whisking from time to time until butter is melted, then cook, stirring constantly until almost as thick as custard. Remember to scoop the mixture from the edges of the pot. Do not force the process by increasing the heat – the eggs will curdle!
Once again use a sieve to strain the curd into a clean bowl to leave curdled egg out. Add the remaining rhubarb juice, stir well. If desired, stir in a splash of grenadine – it will make the color of the curd more intense. Keep the curd in glass jars in the fridge for up to a week.
Serve with scones, hot toast or make mini curd tarts by adding curd into ready sweet pastry cases.