Mix the water and the milk. Dissolve the yeast (the liquid must not be too warm or it will deactivate the yeast)
In a salad bowl, pour the flour and the salt. Mix then add the sugar, the oil and the liquid mixture (water/milk/yeast). Mix coarsely and transfer the dough to a floured surface.
Knead the dough with your hand palm, no stop, during around 10 minutes.
Cover it with a clean cloth and set it aside for 1h30 in a warm place.
Oil the dish and flour it with the semolina (or flour). Place the dough and gently stretch it to the edges.
Prepare the brine by mixing the oil, the water, the sugar and the lemon zests.
Brush the dough surface with the brine then make small cavities with your fingertips all over its surface.
Cover it again and set aside for 45 minutes.
Preheat the oven to 200°C (400°F).
Bake the focaccia for 20 minutes, or until it is well golden.
