Steep saffron strands in 0.5 cup warm vegetable broth for 10 minutes.
Melt 1 tbsp butter and olive oil in a pan, sauté finely chopped onion until soft.
Add arborio rice and toast for 2 minutes until edges look translucent.
Add warm vegetable broth one ladle at a time, stirring continuously and letting liquid absorb before adding more (about 20 minutes).
Stir in saffron broth, remaining butter, and grated parmesan cheese vigorously until creamy and rich; serve immediately.