Step 1Heat the oven to 350 degrees. In the bowl of a stand mixer using a paddle attachment, or in a medium bowl with a hand mixer, beat the butter and sugar until light and fluffy, about 5 minutes. With the mixer running, add the eggs, one at a time. Mix in the vanilla and salt, then fold in the pistachios and flour just until fully incorporated.
Step 2Pipe or spoon the batter into greased madeleine molds. Bake until set and light brown, about 10 minutes. Cool the cookies in the trays 10 minutes before removing from the molds.