In a large microwaveable bowl, combine the melted butter, sugar and eggs, whisking together until combined. Stir in the lemon juice and lemon zest.
Microwave on HIGH for 1 minute. Stir, then continue microwaving in 1-minute intervals, stirring well after each round, for a total of about 6-7 minutes, or until the curd coats the back of a metal spoon and thickens.
Place a fine mesh sieve or strainer over a clean bowl - preferably one with a spout. Pour the curd through the sieve or strainer and gently use a spoon or spatula to stir the curd through the sieve. Discard the large pieces of curd, lemon seeds, zest, and whatever else will not fit through the sieve.
Pour the curd evenly into 2-4 mason jars with lids. Seal the lids and let set at room temperature for about 1 hour to cool down, then refrigerate until chilled. Store leftovers in the fridge for up to 3 weeks.
To serve, spread it on pancakes, waffles, French toast, muffins, scones, pound cake, angel food cake, in between cake layers, as a filling for cupcakes, swirled into cheesecake batter, spread on toast, as a filling for thumbprint cookies, or by the spoonful!
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