Candied lemon peel or whole raspberries (optional)
Using a carrot peeler, remove the zest of 3 lemons, being careful to avoid the white pith. Put zest in a food processor fitted with a steel blade. Add sugar and pulse until zest is very finely minced into sugar.
Cream butter and beat in sugar-and-lemon mixture. Add eggs, one at a time. Then add lemon juice and salt. Mix until combined.
Pour mixture into a 2-quart saucepan and cook over low heat until thickened (about 10 minutes), stirring constantly. Lemon curd will thicken at about 170°, or just below simmer. Remove from heat and cool or refrigerate.
To serve, portion lemon curd into pastry shells. Top with whipped cream; garnish with candied lemon peel or raspberries if you like.