Mix the milk and water and warm it slightly. Dissolve the yeast completely in this milk-water mixture.
Place the flour, salt and sugar on a clean surface and mix. Form into a small heap with a well in the center. Slowly pour the dissolved yeast into the centre, mixing with the flour until all of the yeast water is incorporated.
Knead the dough for 5-10 minutes, like for bread, until it is smooth and elastic. Cover the dough and place in a warm place until it has doubled in size.
In a small saucepan warm the olive oil with some of the rosemary. As soon as the rosemary starts to sizzle, remove saucepan from the heat. Remove the rosemary (throw it away) and let the oil cool.
Grease a rectangular baking pan. Roll out the dough to about 1 cm thick (this thickness is important or your bread layers will be very thick), and wide enough to have the dough overlapping the edges of the pan by about 2-3 cm all around. Place the dough on the pan and cover it evenly with the grapes, leaving very little space.
I used a pie plate because I didnu2019t have the right sized rectangular pan.
Dust the grapes with the sugar and remaining rosemary, then drizzle the olive oil over all of this. Fold the edges of the dough over on top of the grapes around the border, pinching the corners to make the schiacciata rectangular in form.
Bake the schiacciata at 180C for 30 minutes. You might want to place another pan underneath, because the grapes' juice could drip out over the edges of the pan. Let cool and serve with a bit of honey on top.