Preheat oven to 300F.
In a small bowl, combine flour, baking powder and salt. In a larger mixing bowl, combine the eggs, sugar, and lemon zest. Add the melted butter, then incorporate dry ingredients. Slowly add the heavy cream, being careful not to over mix.
Portion the dough into pieces just smaller than a golf ball. Roll each pieces into a snake, then form an 'S'. Place prepared pieces on a greased cookie sheet. Brush the dough with egg yolk then sprinkle lemon zest that's been mixed with a bit of sugar.
Bake for 10-15 minutes or until golden brown, turning the sheet about halfway through baking. Let the cookies cool before removing from the sheet, then enjoy.