Leek, mushroom and thyme risotto

Name: Leek, mushroom and thyme risotto
Cuisine: Australian
Ingredients: 25 gm dried wild mushroom pieces; 1.5 litres hot chicken or vegetable stock (6 cups); 80 ml olive oil (⅓ cup); 120 gm butter, diced; 500 gm portobello mushrooms, thickly sliced; 1 leek (white and pale green parts only), halved and thinly sliced; 4 garlic cloves, finely chopped; 400 gm carnaroli rice (2 cups); 1 tbsp thyme; 125 ml dry white wine (½ cup); 120 gm mascarpone; 50 gm parmesan, finely grated, plus extra to serve (⅔ cup); Finely grated rind of 1 lemon