Crumble the stock cubes into a small saucepan, add 625ml (2½ cups) boiling water and stir to dissolve. Bring to a simmer over medium heat, then reduce the heat to low to keep hot. Finely chop the onion. Crush or finely chop the garlic. Slice the mushrooms. Coarsely chop the parsley and tarragon leaves, discarding the stems. Finely grate the parmesan.
Step 2 — Start risotto
Heat 1 tbs olive oil in a medium saucepan over medium-high heat. Cook the onion and garlic, stirring occasionally, for 2-3 mins until softened. Add the rice and cook, stirring, for 30 secs or until well coated. (You can add 2 tbs white wine to the rice for depth of flavour, if you like. Cook, stirring, until absorbed. It's still delicious without the wine.)
Step 3 — Add stock
Reduce the heat to medium-low. Add the hot stock, ½ cup at a time, to the pan, stirring continuously and allowing the stock to be absorbed before adding the next ½ cup, until all the stock has been used, the rice is cooked and the mixture is thick (this will take approximately 25 mins). The rice should be creamy but still retain some bite.
Step 4 — Pan-fry mushrooms
Meanwhile, heat 20g butter in a medium frypan over high heat. Cook the mushrooms, stirring occasionally, for 3-4 mins until tender. Season with salt and pepper.
Step 5 — Finish risotto
Add the mushrooms, half the cream* and most of the parmesan to the risotto. Increase the heat to high and cook, stirring gently, for 1 min or until slightly thickened. Remove from the heat.
Step 6 — Get ready to serve
Stir most of the herbs and 10g butter into the risotto. Taste, then season with salt and pepper. Cut the lemon into wedges. Divide the risotto among bowls, scatter with the remaining parmesan and herbs. Serve with the lemon wedges.