In a small saucepan, whisk lemon juice, lemon zest, granulated sugar and eggs together.
Place pot over medium low heat and add in butter pieces. Whisk continuously for 7-10 minutes until lemon curd thickens but before it starts to boil.
Remove from heat and pour into jars. Store in refrigerator until ready to use.
Notes
RECIPE NOTE: Be sure to use a whisk that reaches all the way into the corners of the pot you're using to prevent the eggs from cooking/scorching in those corners, giving you lumps. I have found a flat whisk works great for this!Based off a lemon curd recipe from Allrecipes.