Let the yeast dissolve in two tablespoons of warm water. In a medium mixing bowl add the yeast, the flour, the buttermilk, half a teaspoon of salt, a pinch of sugar and a tablespoon of olive oil. Combine all of the ingredients, I use a hand mixer but you can also use your food processor or do it by hand.
Place a kitchen towel over the bowl and let rest for at least one hour at a warm place (better is two hours).
20 minutes before you continue with the dough, clean the pumpkin and cut it into thin slices. The thinner you cut them, the crunchier the pieces get, which is really nice. Roughly chop the blue cheese and cut the Mozzarella into tiny cubes. Set aside.
Preheat the oven to 240°C (460°F).
Part the dough into four equally sized parts. Knead each part by hand before rolling it out and placing each on a sheet of baking paper. If you like the crust to be extra thin, which is great, wait five minutes and roll it even thinner. Equally spread the Mozzarella and blue cheese on the dough. Add the rosemary, pine nuts and pumpkin slices.
Bake one tarte after the other, not at the same time for about 6 to 8 minutes. Serve immediately as they get cold very fast.