Sagra opened three years ago and if there's anything that illustrates the simultaneous extravagance, optimism and naivety that characterised this three-storey Italian food palace, it's the fact that a pizza oven hulked unused in the massive open kitchen. It wasn't until chef Tony Moss came in nine months ago (brief: turn this grand, romantic vision into a viable restaurant) that he saw a place for it.

In March, the pizza oven was moved upstairs to the erstwhile gallery level and Pizza One brought into existence. It's a more casual, less expensive option for Italian food than splashy Sagra. The pizza is great and there are tasty snacks.

The enormous first-floor room wraps around the huge main kitchen so you can peer down on chefs and flashing pans and enjoy the theatre, buzz and flame-licked scents that seep upwards. It's a good option for families and large groups but it's also a clever training-wheels restaurant for those just one promotion away from the $38 main courses being served downstairs.

You need to walk through Sagra to find the stairs to Pizza One, past tables laden with fancier fare: parmesan cream with a bruleed top, pork shoulder with confit grapes, a gleaming tiramisu which we'll get to later.

Pizza One focuses on food from the oven that's eaten with the fingers. The pizza toppings are high quality, taking the produce-focused lead from Sagra, but it's the dough which is the real point of difference. Inspired by American baking pathfinder Nancy Silverton, Tony Moss's dough includes wheat germ and semolina and is fermented for 72 hours.

The resulting pizzas have puffed rims that are both chewy and crunchy, and the dough has deep nutty texture and flavour.

Three of the eight pizzas are vegetarian – the Verde has a pesto base then continues green with roasted zucchini and bright broccolini – but I especially love the Bresaola, with jammy onion, splodges of goat's cheese and paper-thin furls of air-dried beef. Gluten-free bases are available for an extra $5.50.

Other than pizza there's more oven-baked goodness delivered in homely enamel ramekins. Sweet, citrus-spiked pork, raisin and pinenut meatballs are baked in a tomato sauce. Herbed polenta lolls under melted cheese. Soft pumpkin wedges are scattered with toasted pepitas and nuggets of blue cheese. It's all very easy to eat.

Service is good, there's wine by the carafe and, if you do feel like branching out or spending up, you can order anything from the downstairs menu up here. (The converse is not possible; pizza is not permitted in the sparkling main dining room.)

Let's talk tiramisu. The name of this classic Italian dessert means "pick me up", probably because of its bet-hedging triple-whammy hit of caffeine, sugar and alcohol. It's available at Pizza One as a Tiramisu pop, a bittersweet choc-coated ice-cream on a stick that will ruin you for Magnums forever.

Downstairs, the fancy spin on tiramisu is a cylindrical stack coated in a shiny glaze. Bust in and you'll find the traditional mascarpone marsala mousse and coffee-dipped sponge fingers. A contemporary rethink sees the stack sprinkled with sea salt and gold leaf.

I suggest that due diner diligence demands you try both tiramisus. If anyone queries you, just tell them that restaurant research must be rigorous. It's a line I use all the time.

Rating: Three and a half stars (out of five).