Preheat the oven to 200°F. Line two baking sheets with parchment paper, or aluminum foil., In a large bowl, beat together the egg whites, cream of tartar, and salt until foamy., Add the espresso powder, coffee extract, and 1 tablespoon of the sugar, beating until soft peaks form., Gradually add the remaining sugar, continuing to beat until the meringue is stiff and glossy., Pipe the meringues onto the pans using a pastry bag and star tip. Alternatively, drop meringues by large teaspoonfuls onto the pans., Bake the meringues for 1 1/2 to 2 hours, switching the pans (top to bottom, bottom to top) halfway through the bake time. The cookies will feel barely dry on the outside, and will still be soft in the middle., Turn off the oven and leave the meringues inside to cool and dry completely, 1 to 3 hours — or as long as overnight if the weather is humid.