In a large mixing bowl, stir together the melted unsalted butter, brown sugar, molasses, and salt until smooth.

Add in the egg and whisk until thoroughly combined.

Gradually mix in the baking soda and flour until a cohesive dough forms, adding more flour if too sticky.

Divide the dough in half, wrap in plastic, and chill in the refrigerator for 30 minutes.

Preheat oven to 350°F (175°C) and line baking sheets with parchment paper.

Roll out one portion of chilled dough to 1/4 inch thickness and cut out shapes with a cookie cutter.

Place cut cookies on baking sheets, spacing them an inch apart, and bake for 7-8 minutes.

Let cool on baking sheets for a few minutes before transferring to a wire rack.

To prepare frosting, whisk together powdered sugar, vanilla extract, and milk until smooth.

Decorate cooled cookies with frosting as desired.