If you plan on making the delicious Brown Butter Sage and Chestnut Sauce, roast and peel chestnuts first. You can do this up to a couple days in advance. The brown butter sauce is totally optional but really takes this recipe to the next level. If you do not plan on making the sauce, skip to the next step.
Peel and chop pumpkin or favorite winter squash (like butternut, acorn, kabocha, etc.) into one inch cubes. We had about 3.5 heaping cups or about 1 pound total. Set aside.
Set your Instant Pot (pressure cooker) to the sauté function. Add in olive oil, onions, garlic and sauté until aromatic and translucent.
Do NOT wash the rice! Add the raw dry Arborio rice to the aromatics in the instant pot. Stir and toast Arborio rice for 1 to 2 minutes or until all of the rice are well coated with oil.
Add peeled and cubed pumpkin or squash in the instant pot. Season with salt, pepper and thyme leaves.
Pour ½ cup of dry white wine or sherry over the rice and pumpkin in the instant pot to deglaze pan. Stir well. Turn off sauté function on instant pot.
Add in 4.5 cups low sodium vegetable broth (or chicken broth if you do not need to keep vegetarian) (Optional: If you want to cut down on the time for the Instant pot to heat up, microwave the broth for just a minute or two to take the chill out so that it is lukewarm).
Seal the instant pot (or pressure cooker) with lid and make sure the nozzle is set to NO VENT. Set the Instant pot on high for 6 minutes. It takes the instant pot about 10 minutes to get up to pressure and heat up.