Finely grate rind from Grapefruit and juice; you will need 1 cup fof juice.
Place rind, juice, sugar and butter in heat proof bowl. Sit bowl over saucepan of simmering water, making sure the bottom of the bowl does not touch the water.
Stir mixture until butter has melted and sugar has dissolved
Add eggs, whisk over medium heat until mixture thickens and coats the back of a metal spoon (similar to custard).
Pour into a clean dry jar and store in the refrigerator.
Spread toasted muffins with Reduced Fat ricotta and top with Grapefruit butter
TIP: Grapefruit butter can also be used as a filling for small tarts