For the walnut filling, combine the sugar and lemon juice in a saucepan and stir well to mix. Place over medium heat and allow to caramelize, stirring occasionally. When the sugar is a pale amber color, add the honey and butter. Bring to a boil and cook about 2 minutes, until thick bubbles form. Stir in the salt and walnuts. Cool the filling.
For the pasta frolla, beat the butter