The office microwave at noon in February is a battleground, and the people who win it are the ones who brought something worth reheating. This beef barley soup meal prep is built specifically for that moment: a thick, beefy, stick-to-your-ribs soup with tender chunks of beef and chewy pearl barley, portioned into jars or containers that go from desk drawer to microwave to a genuinely satisfying lunch. It costs under $2.75 a serving, it reheats in four minutes, and it makes the sad desk salad people quietly envious. Beef barley soup is also one of the great slow cooker arguments. The long, gentle cook does two things a stovetop pot…