Turn the pizza oven on to begin preheating, as detailed in the instruction manual.
In a large mixing bowl, combine the flour, yeast, salt and sugar. Make a well in the centre, pour in the olive oil and water, and gradually bring together into a wet and sticky dough. Turn the dough out onto a thoroughly floured surface, and use clean hands to knead for a minute or so, just to bring it together into a smooth ball.
Cut the ball of dough in half (it makes enough for 2 pizzas), and gently press one of the pieces out to form the base of one pizza (approx. 30cm in diameter). If using a pizza oven, form the base on a wooden spatula to allow you to transfer it to the oven easily.
Spread the pizza base with some garlic puree and ricotta cheese, and top with half of each of the topping ingredients - the sliced mushrooms, sliced brie, torn mozzarella cheese, and fresh sage. Sprinkle generously with black pepper, and drizzle lightly with olive oil.
Place the pizza in the pizza oven, and bake for around 4-5 minutes, or until cooked to your liking. Repeat with the remaining ingredients to make a second pizza. Best served immediately after cooking.