• Cut the butter into 8 pieces. Next to the stove place a medium course strainer over a bowl. This bowl is for the finished curd.
• Place kumquats and the lemon juice in the bowl of a food processor. Process until the kumquats are puréed, about 1 minute. You may need to stop the processor after 30 seconds and scrape down the sides. Add the sugar and process for about 10 seconds.
• Place the pureed kumquats in a 3-quart saucepan. Taste the mixture before adding the eggs. If it is too tart, add 1 or 2 tablespoons or additional sugar and whisk it in. But remember that the curd is supposed to be tart.
• Add the whole eggs and egg yolks, and whisk to combine. Place pan over medium heat and whisk continuously until the mixture reaches 180 degrees, about 6-8 minutes. Remove the curd from the heat and whisk in all 8 tablespoons of butter. Pour the curd into the strainer and use a large spatula to press the curd through the strainer and into the bowl below. This step will take a while because the curd is thick and has a lot of solids (kumquat skin and seeds).
• Cover the curd with plastic wrap by placing a piece of plastic wrap over the bowl, lightly press it onto the surface of the curd. Place the bowl in the refrigerator and allow to finish cooling.
• Once the curd is cooled it can be used as a spread on toast and biscuits or used as a filling for a tart. This curd is also thick enough to use as a cake filling.

Storage

• The curd can be stored in the refrigerator in an airtight container for up to two weeks. It can be frozen for up to one year in a freezer safe container. When ready to use the curd after freezing place it in the refrigerator the night before to thaw before using.