Chocolate Sandwich Cookies with Cream Filling

I had a fantasy of baking homemade sandwich cookies that taste just like the store-bought kind I ate as a kid. But when they turned out tasting like a grown-up version—rich cocoa, a more delicate crisp, and a vanilla-bean-tinged cream—I had no complaints. A little burst of salt in the dough is the perfect contrast to the sweet filling. These treats taste best the second day, when the icing has had a chance to settle into its new cookie home.