• Preheat the oven to 350℉. Line a 9x13 inch baking pan with parchment paper or spray with baking spray.
• In a mixing bowl, cream together softened butter, white sugar, and brown sugar for about 3 minutes on with an electric mixer on medium speed until fluffy.
  1 cup salted butter, 1 cup white granulated sugar, ½ cup brown sugar
• Add in egg and vanilla and mix well for another 1-2 minutes until fluffy, scraping the sides of the bowl as necessary.
  1 large egg, 1 teaspoon vanilla
• Add in spices and molasses and mix well until it's incorporated completely.
  1½ teaspoons cinnamon, ½ teaspoon ginger, ¼ teaspoon allspice or cloves, ⅓ cup molasses
• Add in flour and baking soda last and mix 1 minute until all the flour pockets are gone and a very soft sticky dough forms.
  3 cups flour, 1 teaspoon baking soda
• Press dough into 9x13 inch baking pan prepared with baking spray or parchment paper. Bake for 23-25 minutes until middle is beginning to crack.

Make the frosting;

• In a small mixing bowl, combine softened butter, powdered sugar, and vanilla and mix until smooth, about 2 minutes.
  ½ cup salted butter, 1 teaspoon vanilla, 2 cups powdered sugar
•  Add in eggnog and mix until creamy and smooth.
  2-3 Tablespoons eggnog or whole milk
• Spread frosting over cooled bars and sprinkle with your favorite holiday sprinkles!