Grate the lemon rind and then cut and juice the lemons, making sure there are no pips.
Crack 8 eggs into a bowl and whisk them until well combined.
In the slow cooker, combine the whisked eggs, white sugar, finely grated lemon rind, lemon juice, and butter.
Turn the slow cooker on High and constantly keep stirring until the butter has completely melted.
Once melted, turn the slow cooker to Low and place a tea towel under the lid. Let it cook for 1 1/2 to 2 hours or until the mixture has thickened to a curd-like consistency. Stir the mixture every 20 minutes or so to ensure even cooking.
Once the Lemon Butter is done, sterilize the jars you plan to store it in by placing them in the oven at 225°F (110°C) for 10 minutes.
Carefully remove the jars from the oven and pour the Lemon Butter into the jars while it is still hot. Put on the lids tightly.
Allow the Lemon Butter to cool completely before refrigerating. It will continue to thicken as it cools.
Enjoy the tangy and velvety goodness of Slow Cooker Lemon Butter (curd) on toast, scones, pancakes, or use it as a filling for pastries and cakes.
Store any leftovers in the refrigerator for up to two weeks.
Notes
The slow cooker method helps to achieve a smooth and creamy Lemon Butter, but it requires constant stirring and monitoring to prevent burning.