Alison DeNisco Rayome/ZDNET Cold brew fans know the process for making this type of coffee is completely different from hot coffee, and can be time-consuming to do at home. But the Cumulus cold brew coffee machine is designed to make only single-cup cold brew, nitro, and cold espresso in a process as easy as using a Keurig -- and it's the only way to make nitro cold brew at home. The machine usually comes at a high price point of $695. But ahead of Mother's Day, it's 15% off  with code MOTHERSDAY15 , making it a great time to buy if you're in the market for a high-end at-home cold brew machine. Also: 5 kitchen tech splurges are totally worth it I tried out the Cumulus cold brew machine at home, and was impressed by the design -- it's tall, but has a slim, stylish profile, and is extremely simple to use. You pop a proprietary pod filled with coffee concentrate into the cylinder at the top, and select from three options: still cold brew, nitro cold brew, or cold espresso.…