Posto is poppy seeds and in Bengali cuisine it is one of the favorite ingredients used. Generally Posto is used with potato to make alu Posto which is quite popular. Posto can be made with variety of other vegetables and also fish and meat. Here I have made this simple and delicious Posto recipe with onions. The recipe is with just a handful of ingredients. Caramelized onions with poppy seeds tastes absolutely divine. All you need is some steamed rice to enjoy this.