Beat the egg whites until stiff. Sprinkle in the salt and sugar. Continue beating until very stiff. Add the lemon juice and continue beating until the mixture shines.
Mix the nuts, flour and vanilla seeds. Fold into the egg whites.
Pour the dough into a piping bag with a large nozzle. Splash 3 cm heaps onto a lined baking sheet. Top each cookie with 1 walnut half. Bake for about 25 minutes at 150°C (approximately 300°F). Remove from the oven, let cool on a wire rack and serve.