McDonald’s is launching a new kind of restaurant, CosMc’s, a retro-style store with treats and customisable drinks including “s’mores cold brew”, “churro frappes” and “turmeric latte” that could rival chains such as Starbucks. The fast food company said it would open its first pilot site in a Chicago suburb near its headquarters this month, as part of efforts to “solve the 3pm slump”, when it gets fewer customers between the lunch and dinner rush. The proposed menu features of a range of speciality lemonades, blended drinks and teas, with flavours such as “popping pear slush” and “tropical spiceade” that can be customised with tapioca pearls, flavoured syrups and energy or vitamin C shots. The drinks will be sold alongside a slimmed-down food offering, which will include the chain’s regular egg McMuffin sandwiches, as well as hash brown and pretzel bites, doughnuts, cookies, ice-creams, and new spicy queso and avocado tomatillo sandwiches. McDonald’s plans to launch about 10 CosMc locations by the end of next year in unnamed locations in Texas. It will study the results of the trial for at least a year before determining whether to expand. The company’s president and CEO, Chris Kempczinski, said CosMc’s aimed to fill a slump in sales the company records in the mid-afternoon, offering drinks too complex for its existing restaurants. “This is a $100bn category that’s growing faster than the rest of [casual dining] and with superior margins. And it’s a space that we believe we have the right to win,” he said. The new stores are named after a part-space alien, part-robot character launched by McDonald’s in the late 1980s. CosMc – who had antennae, more than six arms, and wore a round silver space suit – was featured in a series of adverts until the early 1990s. The CosMc’s pilot was revealed on Wednesday as McDonald’s told investors at a daylong conference that it planned to open nearly 10,000 new restaurants around the world over the next four years. The unprecedented expansion will bring the chain’s total store count to 50,000. That compares with Starbucks, which last month said it planned to expand its global footprint to 55,000 stores worldwide by 2030, up from 38,000 currently. McDonald’s plans to open 900 new stores in the US and 1,900 in international markets that have company operated and franchised restaurants such as Canada, Germany, the UK and Australia. It plans another 7,000 stores in international markets operated by licensees, more than half of them in China.