Bring stock to a low simmer in a saucepan. Keep it just warm and not come to a boil.
Meanwhile, melt butter in a large, wide and shallow skillet. Add onions, parsnips and sage. Saute for 5 minutes before adding arborio rice. Continue to saute until arborio is translucent and starts to brown.
Add white wine, cooking and stirring until it has all absorbed and evaporated. Adding the wine first will ensure that the flavor will absorb first into the rice grains.
Add one cup of broth at a time stirring between additions. Continue to add broth until it has all absorbed. Grains will be plump and a little creamy.
Stir in grated Parmesan cheese and mascarpone. Remove from heat and allow to rest for 5 minutes.
If desired, garnish with additional Parmesan cheese and mascarpone cheese.
If you've tried this recipe, come back and let us know how it was!