Pain Viennois is normally made in the shape of a baguette, though the crust is softer than a baguette, the texture is finer, and the taste is sweeter. The loaves will have horizontal slashes on top, and be glazed with milk and sugar before baking.
It can also be made as rolls (“petits pains”.)
It is made starting with a Poolish.
Up until the 1840s, the French had always risen their bread with a starter, or later with a combination of starter and yeast. When the technique of using a Poolish instead of traditional French starters came along, it made possible faster bread production, and sweeter breads.
How the Poolish technique came to Paris appears to be as yet uncertain.
In 1837, a man named August Zang moved to Paris from Vienna. Around 1838, he started a Viennese bakery at 92, rue Richelieu, introducing to Paris the use of the Austrian steam oven for baking bread in. Some believe that his bakery was also the first to introduce Viennese style bread, risen with Poolish. Other sources say that whether a Poolish was used is unclear.  Zang returned to Vienna in 1848.
Some stories absurdly place the advent of Poolish at the time of Marie Antoinette, as she was Austrian, but the problem with those stories is that they’re confusing the timeline: commercial yeast, required to make a Poolish from, wasn’t available at the time.
. Email to CooksInfo.com from Jim Chevallier, author of “August Zang and the French Croissant: How Viennoiserie Came to France.” 4 June 2009.