Whisk together the yolks, honey, lemon juice, and lemon zest in a small saucepan. Cook the mixture over medium heat, stirring constantly with a wooden spoon, until it thickens, about 5 minutes.
Remove pan from heat. If necessary, strain the curd through a fine-mesh sieve placed over a bowl, to remove bits of egg.
Stir butter into the lemon mixture, one piece at a time, until it is smooth and creamy. Transfer the lemon curd to a clean jar or bowl, seal, and store in the refrigerator for up to 1 week.
Serving Ideas: Serve lemon curd on top of toast, waffles, pancakes, or scones. It is also good dolloped on ice cream or stirred into oatmeal. Try lemon curd as a filling/topping for cakes, cupcakes, jelly rolls, and thumbprint cookies.