Preheat the oven to 325°. Grease 2 or 3 large baking sheets or line the sheets with foil and grease the foil.
In a large bowl, with an electric mixer at medium speed, beat the egg whites, cream of tartar, and salt until frothy. Increase the mixer speed to high and continue beating, adding the brown sugar gradually (in small handfuls) and scraping the bowl once, until the whites form stiff, glossy peaks. (This will take a few minutes.) With a large rubber spatula, fold in the pecans.
Drop the batter by heaping teaspoonfuls onto the prepared baking sheets, spacing them 1 inch apart. Press a pecan half into each, flattening the cookie slightly.
Bake until the macaroons are set and feel hard and crisp, about 35 minutes. Transfer to wire racks to cool completely, then store in airtight containers.