Place a large skillet over medium-high heat and add the oil or butter.
Once the oil is hot or the butter has melted, add the halved Brussels sprouts.
Cook, stirring occasionally, until they are beautifully golden brown and tender, about 10 minutes.
Add the minced garlic to the skillet and cook for one more minute, stirring constantly until it's fragrant.
Pour in the vegetable stock, bring it to a boil, and use a spoon to scrape up any browned bits from the bottom of the pan.
Gently stir in the gigantes beans, along with a good sprinkling of salt and pepper.
Reduce the heat to maintain a steady simmer and cook for about 5 minutes, or until the beans are heated through.
Taste and adjust the seasoning if necessary.
Serve warm, generously sprinkled with the roasted hazelnuts and chopped fresh sage.