First thing first. Wash and slice the mushrooms, mince the garlic, and finely chop the onion.
Add the olive oil and butter to the rice cooker's pot. Turn the rice cooker to its "Cook" setting and melt the butter.
Once the butter is melted and foamy, add the garlic and onion.
Stir occasionally and let them sauté until the onion turns transparent.
Add the Arborio rice to the pot. Stir it well to coat each grain with the butter and oil mixture.
Let the rice cook for a few minutes until it turns slightly opaque.
If you want to use wine, stir gently into the rice cooker. Allow the wine to be mostly absorbed by the rice.
Then, add the sliced mushrooms into the rice mixture.
Pour one ladleful of the hot broth into the cooker at a time. Stir after each addition until the liquid is mostly absorbed before adding more.
Now close the rice cooker lid and let the risotto cook. This usually takes about 10-15 minutes.
Once the cooking is complete, check the risotto's texture. It should be creamy, and the rice should be tender but still slightly firm to the bite.
Turn off the rice cooker and toss in the grated Parmesan cheese.
Season the risotto with salt and pepper to taste.