Preheat oven to 350 degrees F.

In large bowl with electric mixer, beat together butter and sugars until light and fluffy, about 2-3 minutes.

Add eggs, one at a time, beating until well combined.

Add molasses, beating until well combined.

In medium bowl, combine flour, baking soda, spices, and salt.

Add flour mixture to butter mixture, beating until well combined.

Using a cookie scoop, form dough into 1" balls, and roll them in sugar.

Place them on baking sheet lined with parchment paper.

Be sure to space them at least 3" apart, as they will spread.

Bake in preheated oven for 9-10 minutes. Don't over bake - they will be hard if you do! They should look cracked and edges should be set.

Let cool for 10 minutes on baking sheet, then cool completely on cooling rack.

To make the eggnog buttercream:

Beat butter with electric mixer until light and fluffy, about 2-3 minutes.

Add powdered sugar, beating until well incorporated.

Add eggnog and vanilla, beating until combined.

Place buttercream in piping bag or plastic baggie with one corner cut off.

Pipe buttercream over half of the cooled cookies, then top with remaining cookies.

Alternately, you can spread the buttercream on with a knife.

Serve and enjoy!

Keep in airtight container for 3-4 days.