1. Set a fine-meshed sieve over a bowl. Pour 2 inches of water into a pan and bring to a simmer over low heat. In a bowl that fits over pan without touching water, mix juice and zest, eggs, butter, salt and 1 cup sugar. Cook, stirring constantly with a heatproof flexible spatula, until butter has melted, sugar has dissolved and mixture thickens enough to coat the back of a spoon, 20 to 25 minutes. (Do not allow it to boil.) Pour through sieve into bowl; press plastic wrap onto surface of mixture. Chill for at least 10 hours. (Curd will thicken as it cools and can be made up to 5 days ahead.)

2. Preheat oven to 350ºF. Place tart shells on a baking sheet; bake for 5 minutes. Let cool.

3. Whip cream with 1 tsp. sugar until soft peaks form. Cover and chill. Just before serving, put a heaping teaspoon of lemon curd into each shell. (Cover and chill any extra curd.) Pipe or spoon whipped cream on top of each tart. Serve immediately.