Heat water, add sugar, stir until dissolved. Raise the heat to bring the syrup to a boil. Add lemon juice, condensed milk and butter.
Cook over low heat for 20 minutes, stirring. At the end, add nuts (walnuts can be chopped a little, the rest are whole).
Let it cool down a bit. Pour the mass into a form covered with a film and put it in the freezer until it hardens (if you like soft nuts, then do not keep in the freezer). Cut as desired. I got 36 candies depending on the shape.