Preheat the oven at 180C.
In a small bowl, mix the yeast with 25 ml of the water, a tablespoon of flour and the yeast. Cover with cling film and let it rest for 10 minutes. It should double in size and start to foam.
Add the rest of the white flour and the spelt flour into the bowl of a standing mixer. Add the yeast mix and start mixing at low speed, adding the water gradually. If the flour is good, it should absorb all the water. Continue mixing at medium/high speed for about 5 minutes, then add the sugar and continue mixing for another 5 minutes, until the dough is smooth and silky. Add the olive oil gradually and finish the mixing process. The dough will be quite wet, but it should come together nicely and the high hydration will create that beautiful open crumb in the final product.
Transfer the dough into a lightly oiled bowl and cover with cling film. Allow it to rise until at least double in size (about 1 hour, depending on the temperature of the room).
Meanwhile wash and tap dry the grapes.
Prepare 2 trays, by lightly covering them with olive oil.
Put some olive oil on your working surface, tip the dough and divide it in two. Gently press each piece of the dough, then use your whole palm to lightly press the dough on the oiled surface until it reaches the size of the tray. Move the dough into the ray and - again - lightly press it towards the edges of the tray. Add the grapes and gently push them into the dough. Allow the dough to rise again for at least 20 minutes, then - again - gently push the grapes inside the dough. Add the oregano and sprinkle an even layer of caster sugar on top.
Bake at 180C (fan) for 25-30 minutes.
Serve warm, with creme fraiche on the side.