While everything is heating up, chop your onions and prepare your brussels sprouts. For the onions, halve them cutting through the root end. Cutting them this way will allow you to keep the onion in tact while slicing further. Remove the outer skin. Now, lay the onion on its side, cut side down for stability. Start by cutting half-moon shapes from the opposite end of the root. Make sure the slices are relatively thin since we will want to caramelize these. Once all the onions are cut, add them to the saute pan along with half a teaspoon of salt. Stir and let those cook, stirring occasionally. Once they turn translucent, turn the heat down to medium-low and keep cooking. The sweetness in the onions will start to caramelize and turn a nice golden brown. This should take about 20-25 minutes.