Sauté: Select the sauté button on the Instant Pot. When hot, add the butter. When the butter is melted and begins to sizzle, add the onion. Cook for about 2 minutes, or until the onion has begun to soften. Add the garlic and Arborio rice and continue to cook for 1 minute longer, stirring frequently. Gradually add the chicken stock, stirring and scraping up any browned butter or onions that have formed at the bottom of the pan.

Pressure Cook: Secure the lid on the Instant Pot and ensure the steam release valve is set to the sealing position. Select the pressure cook or manual setting, set to high pressure, and set the timer to 10 minutes. When the time is up, let the pressure release naturally for 10 minutes. Carefully turn the valve to the venting position to release the remaining steam.

Finish the Dish: Follow the package directions to steam the frozen broccoli on the stovetop or in the microwave. Drain it thoroughly and add it to the rice along with the cheese. Stir the broccoli and cheese into the rice until the cheese has melted and is evenly distributed. Taste and add salt and pepper, as needed.