To brown the butter, melt it completely in a pot over medium heat. It will begin to rapidly crack & sizzle - let it do this while stirring occasionally.
After a few minutes or so, the butter will calm down and begin to foam up in the pan. Swirl the pan around, looking for brown bits & checking if the butter is golden brown. Once golden brown, immediately remove from the heat and pour the butter into a large bowl.
Place the bowl in the fridge and gently stir every 10-15 minutes to ensure an even cool. Meanwhile, whisk together the all purpose flour, salt, cinnamon, ginger, nutmeg, and all spice. Set aside.
Once the butter has reached a room temperature-like consistency, it is ready. Beat the brown butter & granulated all-purpose sweetener together until light & fluffy.
Add the egg yolks, vanilla extract, & molasses and beat until combined, scraping down the bottom & sides of the bowl as necessary.
Add the dry ingredients to the wet ingredients & beat until combined. Gradually stream in the heavy cream or milk if the dough looks a little dry & crumbly. You want it to completely come together into a smooth dough.
Once combined, divide the dough in two & wrap tightly in plastic wrap. Refrigerate for at least one hour.
When ready to bake, line a baking sheet with parchment paper & set aside.
Working with only one half of the dough at a time, gently roll it out on a lightly floured surface until it’s about ¼ inch thick. Use a cookie cutter to cut out as many cookies as possible, spacing them on the prepared baking sheet about an inch apart.
Place the baking sheet in the fridge while you gently re-roll the scraps and repeat. Repeat this process with the other half of the dough as well.
Place the baking sheet in the freezer while you preheat your oven to 350F. Bake the cookies for 8-12 minutes until lightly golden. The bake time will vary depending on the size of the cookie cutter you used.
Let cool on the baking sheet for 5 minutes then carefully transfer to a cooling rack to cool completely.
For the royal icing, beat together the confectioners sweetener, meringue powder, water, and vanilla extract, starting on low speed for 30 seconds, then at high speed for 4-5 minutes until stiff peaks form. You might need to add more water (to thin) or more sweetener (to thicken) depending on desired consistency.
If desired, separate the royal icing into different bowls & mix with food coloring. Use a piping bag to decorate the cooled cookies. Add other decorations like sprinkles, candy, etc., and enjoy!