In a saucepan over medium heat, bring the stock to a simmer and add the saffron. Reduce the heat to low and keep the stock warm.
In a large saucepan over medium-high heat, warm the olive oil. Add the onion and garlic and cook, stirring occasionally, until softened, 4 to 5 minutes. Add the rice and stir until each grain is well coated with oil and translucent with a white dot in the center, 3 to 4 minutes. Add the wine and stir until it is completely absorbed, about 2 minutes.
Begin adding the stock 1 cup at a time, stirring frequently after each addition. Wait until the stock is almost completely absorbed before adding more.
When the rice is tender but firm to the bite, after 20 to 25 minutes, stir in the butter. Add more stock if needed so the rice is thick and creamy. Season with salt and pepper and sprinkle with the parsley.