Warm the stock in a saucepan and keep it just below a simmer. Crush the saffron threads into a small ladleful of warm stock.
Heat the olive oil and 1 tablespoon of butter in a wide skillet. Cook the onion until soft but not browned, about 5 minutes.
Cook the Rice:
Add the rice and toast for 2 minutes, stirring until the grains look translucent at the edges. Pour in the wine and stir until absorbed.
Add warm stock one ladle at a time, stirring frequently and waiting until nearly absorbed before adding more. Add the saffron stock halfway through. Continue until the rice is tender and creamy, 18 to 22 minutes.
Finish and Serve:
Remove from the heat. Stir in the remaining butter and parmesan, season with salt and pepper, and rest for 2 minutes.
Serve immediately while the risotto is loose enough to spread gently on the plate.
Notes
Use warm stock throughout the cooking process.
Stir often but gently to release starch without breaking the grains.