We've all come to expect blazing comparable store sales growth from the likes of Starbucks (NASDAQ:SBUX) and Chico's FAS (NYSE:CHS) -- but McDonald's (NYSE:MCD)? Believe it. Last night, the world's largest fast-food chain reported a remarkable 11% increase in July comparable store sales.

Saturated fat and all, consumers apparently agree with McDonald's new slogan, "I'm lovin' it." On a constant-currency basis, comp sales increased by 7%. This includes all of McDonald's restaurants, including Chipotle, Donatos, and Boston Market. But even isolating just the McDonald's brand alone, comps were up a solid 4.2% on higher sales of its flagship Big Mac sandwich, premium chicken sandwiches, and breakfast products such as the terrific new McGriddle sandwich.

In reaction, the stock is up more than 6% today, to $23 and change. This puts McDonald's almost 100% higher than its March low of $12. Amazing that only a short five months ago, investors were practically in hysterics over the company's first quarterly loss in 38 years (mostly due to accounting write-downs; the cash loss was much less severe).

Admittedly, few expected McDonald's to right its ship so quickly. New CEO Jim Cantalupo stepped in and quickly implemented a common-sense strategy of maximizing sales at existing locations through higher-quality food and better service. So far, so good, based on the comparable store sales we're now seeing.

Another good sign is the company's operating cash flow, which year-to-date is at $1.24 billion, up slightly vs. a year ago. Cantalupo has been using this cash to pay off debt -- $400 million so far this year.

In retrospect, McDonald's was a screaming bargain in the mid-teens. A few Fools happened to see it, too. One month after the stock hit bottom, Bill Mann applauded incoming CEO Cantalupo's new slow-growth strategy. Less than one month later, David Gardner waxed bullish on the shares: "There are significant challenges, but you're buying a premiere brand name during an out-of-favor period, piloted by a turnaround CEO."

That out-of-favor period didn't last long, however. Analysts now expect McDonald's to earn $1.34 per share this year, putting the stock at a forward P/E multiple of 17.6. For a company pursuing an explicitly slow-growth strategy, the stock appears to be back in the range of fair value.