To make the dough, in a large bowl add the yeast and warm water and whisk until just combined. Allow to sit for 5-10 minutes for the yeast to foam and bubble. If the yeast does not foam, your water may be too hot, too cold, or the yeast may be expired.

Add in the flour, salt and caster sugar and mix well with a wooden spoon until it is incorporated well. The dough will be wet and sticky, which is perfect for this dough.

In a separate bowl, coat the inside with 4 tbsp of extra virgin olive oil, making sure the bottom and the sides of the bowl are completely covered. Transfer the dough to the oiled bowl and give it a gentle turn so that the dough is covered in oil, cover with plastic wrap and place in a warm place for 2 hours, allowing it to double in size.

To make the filling, add butter in a large saucepan and melt over low heat. Cook the mushrooms in batches for 3-5 minutes or until they are slightly golden brown. Remove from the pan and set aside.

To the same saucepan, add olive oil and cook the garlic, onion and chiili flakes for 2-3 minutes over medium heat until the onion becomes translucent and soft. Add spinach and cooked mushrooms and stir until the spinach starts to wilt, about 5 minutes. Turn off the heat and allow to cool.

Grease a baking pan with butter, lightly coat your hands with a little olive oil and carefully transfer the focaccia dough to the baking pan. Using your hands to carefully stretch out the dough, stretching it out to the sides. Cover with plastic wrap or towel and place in a warm spot for 30 minutes, allowing it to puff up.

Preheat the oven to 180c. Remove the plastic wrap and drizzle the remaining extra virgin olive oil over the top. Oil your hands with a little more olive oil and gently dimple the dough with your fingers.

Layer the potato rounds on top of the dough followed by spooning the mushroom and spinach. Tear the Squacquerone over the top and season well with salt, pepper, rosemary and an extra drizzle of extra virgin olive oil.

Bake in the over for 45-50 minutes until golden, or until the top of the focaccia is nice and golden and the edges are nice and crispy.