Once mixture has thickened, whisk vigorously and add butter, one pat at a time, adding each next pat when the previous one begins to melt. Remove from heat immediately.Storing Lemon CurdTo store lemon curd, place it in a tightly sealed container. Refrigerate once cooled. It will keep well for about a week in the refrigerator. To freeze the lemon curd, once cooled, place it in a tightly-sealed container. It will keep several months in the freezer.Uses for Lemon CurdUse this lemon curd as:A sandwich filling for two keto lemon cookiesA topper for a keto mug cakeA topping for a no-bake keto cheesecakeA swirl-in for keto cheesecake popsiclesWhy isn't my lemon curd thickening?If your lemon curd isn't thickening properly, try turning up the heat from simmering water to a gentle boil, or switch to a mixing bowl that sits closer to the water.Why did my lemon curd scramble?If the curd thickens too quickly, it can scramble. This can be saved by blending in a blender until creamy again. Alternatively, if it scrambles just slightly, you can strain it through a fine mesh sieve so that the scrambled bits get left behind. Lemon curd can also scramble if it isn't whisked vigorously enough. Be sure to use a large whisk with very firm tines.These Keto-Friendly Lemon Bars Are a Dose of Sunshine