Make the tart shells: In a large bowl with a spatula, blend softened butter and sugar until smooth. Add eggs and vanilla, switch to a whisk and whisk until smooth. Add flour and salt and stir with a spatula until the mixture forms into a soft dough. Form dough into two equal balls and wrap each in plastic wrap and refrigerate for 45 minutes up to 1 hour.

Lightly grease 24 standard muffin cups. Roll 2 tablespoons of dough between the palms of your hands into 24 balls, and place them in the muffin cups. With your thumb press the dough into the bottom and about half way up the sides of each cup. Flour your fingers as you go if necessary. The dough may seem thin but it will puff up when baked. Place the pans in the freezer to allow the tarts to freeze while preheating the oven and preparing the filling.

Meanwhile, place a rack on the second rung from the bottom of the oven then preheat the oven to 350 degrees F.

Make the lemon curd filling: In a medium bowl whisk sugar, cornstarch and lemon zest. Whisk in lemon juice, eggs and cooled butter until smooth. Carefully and evenly spoon about 1½ tablespoons of the filling into each frozen tart shell. Evenly distribute any remaining filling taking care not to over-fill the tarts.

Bake on the lower rack for 15 to 20 minutes or until just lightly golden and set. Cool for 5 minutes in the pan. Use a thin knife to gently lift the tarts from the pan and transfer them to a rack to cool completely. Store tarts in an airtight container in the refrigerator. Serve cold or at room temperature. Just before serving garnish each tart with a fresh raspberry.