Authentic Polish Walnut Cookies (Ciasteczka Orzeszki)

Ingredients

• Dough:
• 4
  ounces (1 stick) butter (unsalted, softened)
• ⅛
  teaspoon salt
• ⅓
  cup sugar
• ¼
  cup confectioners sugar
• 1
  teaspoon vanilla extract
• 1
  large egg (room temperature)
• 1 ¼
  cups all-purpose flour
• Filling #1:
• 1
  teaspoon cocoa
• 1
  teaspoon rum (dark)
• 1
  cup jam (apricot)
• 1
  tablespoon milk
• ¾
  cup walnuts (ground, not chopped)
• OR
• Filling #2:
• 4
  ounces/1 stick butter (softened)
• ¾
  cup confectioners sugar
• 7
  ounces walnuts (ground, not chopped)
• 1
  shot vodka
• Milk as needed to make a moist filling