In a bowl, with an electric mixer (fitted with whisk attachment) on high speed, beat egg whites and cream of tartar until thick and foamy. Gradually add sugar and continue to beat until mixture holds stiff, shiny peaks. Beat in vanilla and espresso powder.
Spoon meringue in 1 1/2- to 2-inch-wide mounds, about 1 inch apart, onto cooking parchment-lined or buttered and floured 12- by 15-inch baking sheets (see notes). Gently place one coffee bean on each mound.
Bake in a 200 oven until meringues are light brown and give slightly when gently pressed, 1 1/4 to 1 1/2 hours; switch pan positions halfway through baking. Turn off heat and leave meringues in closed oven for 1 hour.
