If you never noticed that unsalted butter existed, you're probably not a baker.
The vast majority of American butter is sold salted, because it's more stable and can last a month or two longer before spoiling. Salting also can mask "off" flavors that butter picks up readily, even under refrigeration.
Unsalted butter has a shorter shelf life and so can't be kept around as long. In theory that should mean unsalted is likely to be fresher, as long as you have a conscientious grocer or you check expiration dates.
Bakers use unsalted butter for another reason: taste. Without the salt — more than a half teaspoon per stick, though amounts vary by brand — the rich dairy flavor shines more brightly.
In this recipe, inspired by Russ Parsons' ?"How to Pick a Peach," chunks of cold, unsalted butter help a mixture of eggs, lemon juice, zest and sugar cook slowly enough to become a ?glossy, rich pudding instead of a curdled mess. The graham cracker "crust" lining the ramekins was chosen for sheer simplicity. You could swap out the graham crumbs for your favorite plain cookie (like vanilla wafers or gingersnaps) or ?bake a real tart crust.
For the crust:
1 1/2 cups graham cracker crumbs
6 tablespoons unsalted butter, melted
1/3 cup sugar
1/4 teaspoon Asian five spice powder or cinnamon (optional)
For the curd:
2 large eggs
2 large egg yolks
1/2 cup sugar
1/4 teaspoon salt
Zest of 1 lemon
1/2 cup lemon juice
6 tablespoons cold, unsalted butter, cut into chunks
To make the crust: In a small bowl, combine crumbs, 6 tablespoons melted butter, sugar, spice (if using) and a pinch of salt. Combine until mixture resembles wet sand. Press into ramekins or low baking dish, and chill.
To make curd: Beat the eggs, yolks, sugar and salt in a small saucepan until smooth and light-colored.
Add the lemon zest, lemon juice and butter, and cook over medium heat, stirring constantly until the butter melts, about 2 minutes.
Reduce the heat to medium-low and continue cooking and stirring for about 5 minutes, or until the curd is thick enough to coat the back of a spoon and your finger leaves a definite track when you draw it across the spoon. The curd should resemble a thick hollandaise. (Optional finesse step: Pour it through a fine-mesh strainer into a chilled bowl.)
Spoon the curd into the prepared ramekins, or crust, and smooth the top with the back of a spoon. Refrigerate at least 1 hour to set the curd. Serve cold, topped with raspberries or strawberries if desired.