What kind of building do you get when you cross the über-cool, urban minimalism of the Apple stores with the indulgent, diet-busting excess of the Cheesecake Factory restaurants?

Would you believe an architectural confection that is as visually sublime as it is intellectually rich?

I'll admit that when I first heard that the popular suburban temple of caloric overload was touching down at 15th and Walnut Streets, the news didn't exactly stoke my appetite for good design. I imagined a generic box, done up in flat, lifeless stucco the color of American cheese, elbowing its way onto a corner that has been occupied for the better part of a century by three ordinary, but charming, commercial buildings.

But the architecture gods have smiled on Philadelphia.

When the Cheesecake Factory takes up residence here late next year, it will be one of several tenants in a dynamic new building designed by a top-notch firm, Bohlin Cywinski Jackson, which created Apple's retail prototype and executes all its stores, including the one on Walnut Street. That BCJ's building will house this particular dining chain is the least interesting thing about it.

Given the firm's success with the famous - and now trademarked - Apple cube in Manhattan, some might be expecting a variation of that glass box here. But the architects, who work in BCJ's Philadelphia office, have come up with something more gratifying: an original design that responds to its surroundings in a deeply informed way. Their sophisticated Philadelphia glass box promises to be one of the city's finest new buildings.

It's true that you can still see evidence of the Apple lineage in the three-story design, which received a green light last month from the zoning board. Like the New York cube, it is an all-glass, modernist building. But the similarities end there.

Because the New York cube is meant to appear as weightless as a lone soap bubble on its open plaza, it is supported by nearly invisible glass fins. In contrast, the Cheesecake building will be hemmed in by masonry heavyweights from the early 20th century. The designers, Frank Grauman and Andrew Moroz, knew their bantam of a building needed to convey a toughness and gravitas if it were to hold its own against such formidable neighbors.

The most notable is the old Drexel & Co. headquarters across the street. That rusticated stone building, which now houses a health club on its lower floors, was modeled on Florence's Strozzi Palace.

The Cheesecake building flexes its muscles in a modern way, by flaunting its bones and skin. Extra-thick, extra-clear glass panels appear to slide across the Walnut Street facade like barn doors, revealing the massive steel columns and beams that will support the building.

Most glass buildings are riffs on lightness, but here the architects intentionally emphasize the thickness of the transparent skin by making deep cuts into the surface.

At the eastern end, a two-story niche announces the entrance to the restaurant, which will occupy the entire second floor. The opening is balanced by a second-floor dining deck carved into the corner. Below, another notch in the surface will serve as a door for one, or possibly two, ground-floor retailers. Access to the third floor, which can be subdivided, is from a door on 15th Street.

These days, when so much retail has migrated to the Web, it's rare to see a new commercial building on an urban street. Despite the Cheesecake Factory's association with the building, it wasn't the impetus for the project, being built by New York's Midwood Investment & Development.

The company, which has been buying up Center City retail properties since the late 1990s, found it increasingly difficult to rent its three small buildings, which are narrow and eccentric. Eventually, Midwood decided it would be better off with one building with large open floors, company president John Usdan told me.

At that time, Cheesecake Factory hadn't signed on, so Midwood told BCJ to design a generic interior that could handle a variety of tenants. The company briefly considered including a residential tower but concluded it would be uneconomic on the small site, 80 by 186 feet. In keeping with modern preferences, each floor is 20 feet high.

The Cheesecake Factory is not exactly the sort of tenant you would expect to be drawn to such a sleek building. Famous for its supersize portions, the restaurant has repeatedly won the "Xtreme Eating" award from the nonprofit Center for Science in the Public Interest for its "food porn" - dishes that exceed recommended daily allowances of salt and fat, like its 3,210-calorie Bistro Shrimp Pasta.

Though we may be loath to admit it, it was only a matter of time before the Cheesecake Factory colonized a patch of this fat- and salt-loving town. It is one of the most profitable restaurants in the country, yet like so many suburban chains, it is running out of acceptable highway and mall locations. The only way to maintain its growth is to migrate to the city.

No doubt, some here will mourn the loss of these three commercial buildings, which contribute to Walnut Street's special character but are not considered historic. But cities change: That corner building previously was the nine-story Hotel Flanders, until it was cut down to a two-story retail building sometime in the '40s or '50s.

The new building is a rare case in which the architects have cooked up a replacement that is even better than what was there before.

Contact Inga Saffron at isaffron@phillynews.com, 215-854-2213 and on Twitter @ingasaffron.