Ingredients:
    125 g (1/2 cup AKA 1 stick) unsalted butter, room temperature
    1/2 cup confectioners' sugar
    1/2 teaspoon vanilla extract
    1/4 teaspoon salt
    1/2 cups all-purpose flour, plus as much as needed for rolling
    1/2 cups rice flour or tapioca starch 
    Zest from one etrog (citron), or Meyer lemon, or dried yuzu (Japanese citron). Or: mix in 1/4 cup of candied citron peel

Instructions: 
- Using your tool of choice (fork, wire whisk or an electric mixer) beat tougher the butter, sugar, vanilla, and salt until smooth.
- With mixer on low speed, add flour, mixing just until a dough forms. Stir in desired mix-ins.
- Divide dough in half; wrap with a plastic wrap and gently roll each into a 1 1/2-inch-diameter log. Place in the freezer for at least one hour (or store up to several months so that you can just slice and bake a few cookies on demand whenever unexpected company is coming)
- Preheat oven to 350 degrees.
- Unwrap logs, and using a French knife, slice dough 3/8 inch thick (if dough crumbles, leave at room temperature 5 to 10 minutes). Arrange slices, about 1 inch apart, on baking sheets.
- Bake until lightly golden around the edges, about 15 to 20 minutes.
- Cool on baking sheets 1 to 2 minutes; transfer to a wire rack to cool completely.