Beat the egg whites with the lemon juice and salt until very stiff. Then gradually pour in the sugar. Set aside 2 tablespoons of the egg whites. Then carefully fold in the ground nuts with a flat whisk or wooden spoon. Work through the mixture again with the spatula so that all the nuts are carefully worked in.
Pour the dough into a piping bag with a No. 10 star nozzle and pipe the macaroons onto sheets lined with wafers. Pour the egg whites into a second bag with a small nozzle and use it to spray a small dab in the middle of each macaroon. Then gently press in a whole hazelnut.
Bake in a preheated oven at 130 ° C for about 10 to 15 minutes - the macaroons should be dry on the outside and still a little juicy on the inside.