I often use store-bought lemon curd, simply because it’s quick and easy, but you really can’t beat the homemade variety. I recently made some, using a slightly modified version of Miette‘s recipe:
1 cup sugar
1/2 cup lemon juice
zest of one lemon
7 egg yolks
1/2 cup unsalted butter, cut into pieces
Whisk together all but the butter in a heat-proof bowl. Set the bowl over a pot of boiling water. Cook, stirring occasionally, until the curd is thickened. (If you stir it with a wooden spoon, remove the spoon and draw a line on the back with your finger, the line should stay).
Strain the curd, and let it sit for 20 minutes. Using a hand mixer, beat in the butter.
Cover with plastic wrap, so that the plastic touches the top of the curd. Refrigerate until chilled, and use within a week.