In a stand mixer, combine the flour, salt and yeast, keeping the salt from touching the yeast directly. Add the water and mix until all the flour is picked up.
Knead until the dough is very smooth with no ripples and passes the windowpane test.
Add the softened butter and knead until it's fully worked in.
Cover with plastic wrap or a plate and let rise until doubled, about 1 hour. It can take as little as 30 minutes in a hot kitchen or 2+ hours in a cold one.
Punch the dough down and divide it into 24 equal pieces (or 12 pieces cut in half). Shape each piece into a ball.
Starting with the first ball, roll it flat into a circle. Top with about 1/12 of the blue cheese and the slices from about 2 grapes.
Roll a second ball into a circle about the same size, lay it on top, and pinch the edges to seal. Press or roll it flatter. Repeat to make 12 flatbreads.
Heat a cast iron skillet or heavy pan over medium heat and cover the bottom with neutral oil. Cook the flatbreads until golden brown, about 3 to 5 minutes per side, pressing down if they puff up.
Cool on a wire rack, slice each flatbread into fours, and serve hot.
