Take cookies in a blender and crush them. Melt butter in a sauce pan, Add powdered cookies and mix well. Spoon this in a pan and press evenly so it is well lined. Chill in fridge till needed.
Take gelatin in a bowl, add in water and let it soak for 5 mins. Now take it in a sauce pan and heat gently so it is melted.
Now take condensed milk, lemon juice and zest. Mix well. Add food colouring and lemon essence if needed.
Add the melted gelatin to this and mix well.
Pour this over the crust and chill in fridge for 3 to 5 hours.