In a small bowl, mix together the stout beer of choice (cold) and the simple syrup (also cold) with a whisk. Pour this mixture into the popsicle molds, ice cube trays, silicone molds or small plastic cups. Place into the freeze, making sure the mold/container is level. Freeze for 6 – 12 hours in a 0°F | -17.7°C or below freezer, until completely solid. Since 40% alcohol cannot freeze until 173°F | 78°C, the higher the alcohol content of the beer might change the texture of the finished popsicles.