For cookies:

1. Beat the butter and sugar together in a stand mixer until light and fluffy (about 3-5 minutes). 
2. Wisk together the flour, baking soda, spices, and salt in a medium bowl.
3. Beat the egg, molasses, vanilla, and bourbon into the butter and sugar mixture.
4. Slowly beat in half of the flour mixture. Mix until combined, and then add in the remaining flour and mix until just combined.
5. Cover the bowl in plastic wrap and chill for at least 1 hour. 
6. Once chilled, preheat the oven to 350 degrees. Roll the dough into 1 1/4 inch balls and roll each ball into the granulated sugar. 
7. Placed the balls 3 inches apart onto baking sheets and bake for 14-15 minutes. 

For the French buttercream:

1. Combine the water and sugar together in a small or medium saucepan and melt on low heat. Once the sugar has melted, turn the heat up to medium-high heat. Cook until the sugar reaches the soft ball stage or gets to 240 degrees.
2. While the sugar is heating, beat the egg yokes until they are light and foamy.
3. Once the sugar reaches 240 degrees, quickly add it to the egg yokes and beat until the bowl has cooled. About 5-6 minutes.
4. Add in the butter 1 tablespoon at a time and beat thoroughly between each tablespoon.
5. Finally, add in the vanilla and bourbon and beat for another 5 minutes. 
6. For the assembly, if you are going to serve right away and want delicious messy cookie sandwiches, pipe the buttercream onto one cookie and top it off with another. If you want more long-lasting and elegant cookies, pipe a rosette on top of each cookie.