Brioche dough
In the bowl of a stand mixer, dissolve the yeast in the buttermilk with the two pinches of sugar. Let it rest for 10 minutes or until the mixture foams.
Add the melted butter, egg, and vanilla seeds, and mix.

Add the flour, sugar, and salt.
Mix on low speed with the hook for 6 minutes.
Add a little flour if the mixture is too sticky.
Form a ball with the dough and place it in an oiled bowl, turning it to coat it evenly with oil.
Cover and let it double in volume, about 1 hour.

When the dough has doubled, place it on a floured surface and roll it out into a rectangle of 12 x 14 inches (30 cm x 35 cm), with the long side facing you.
Mix the soft butter, brown sugar, and cinnamon with a fork and spread the mixture over the dough, leaving a 1/2 inch (1 cm) border, facing you.
Brush this border with a little water.
Roll the dough and press the edges to seal it.

Cut the cylinder into 12 portions and let them rise under a cloth for 30 minutes.

Preheat the waffle iron.
Place a portion of brioche dough, close the waffle iron, pressing slightly to spread the dough, and cook until the waffle is golden brown.