Preheat oven to 350 degrees F (176 C). In a bowl, cream butter. Then add sugar and egg and mix again. Add molasses and mix until well combined.
Add flour, salt, baking soda and spices to a sifter and gradually sift over wet ingredients while mixing. Beat until well combined, scraping sides as needed.
Chill dough for 10-15 minutes while oven continues to preheat.
Scoop rounded 1 Tablespoon balls of dough onto a parchment-lined cookie sheet – press down slightly with your finger to flatten. (Rolling in sugar is optional, but not necessary.)
Bake for 9-11 minutes, being careful not to over bake. Cook completely on a cooling rack and then prepare buttercream by creaming butter and zest, then adding in powdered sugar in 1/2 cup measurements. Thin out to desired consistency with orange juice. Mix until well combined and fluffy, scraping down sides as needed.
Once cookies are cooled, place a generous amount of buttercream on the bottom of half the cookies and top with the other half (you will have leftover frosting). Store in an airtight container for up to a few days. However, they’re best when served fresh.
*Make this recipe vegan and dairy-free by subbing the butter for non-dairy butter and the egg for a flax egg. *Nutrition information is a rough estimate.