So delicious !
It's a "brioche" too, but filled with "praline". A praline is an almond covered with sugar.
Where can I find it ?
In a gook bakery. You can also find it in a supermarket, close to the bread and the fresh cakes. But be careful, it's better to spend one or two euros more for a good one. If you don't buy a good quality Saint-Genis, the pralines will be so hard you can't bite into.
You'll find more Saint-Genix in the Drome (close to Valence, Romans), it's a speciality from this region. (sout east of France, south of Lyon)
How long can I keep it ?
A few days at room temperature.