Langues-de-chat -- "cat tongues" -- are classic French butter cookies.
Preheat oven to 375 degrees. Sift together flour and salt in a small bowl; set aside.
Put butter into the bowl of an electric mixer fitted with the paddle attachment; mix on medium speed until smooth and creamy. Mix in sugar. Add eggs, 1 at a time, mixing well after each addition. Mix in vanilla. Fold in flour mixture.
Transfer batter to a pastry bag fitted with a 3/8-inch plain round tip (such as Ateco #804). Pipe 2-inch lengths, about 3/4 inch wide (the ends should be slightly wider than the center), onto baking sheets lined with parchment, spacing about 1 inch apart. (Batter should be refrigerated if not being used immediately.)
Bake until just golden around edges, 10 to 12 minutes. Let cool on sheets 3 minutes. Transfer to wire racks; let cool completely. Cookies can be stored in airtight containers up to 3 days.