Peel the onions, cut off the ends, cut in half so you have half moons, then slice thin julienne-style.

In a large pot over medium-high heat, melt the butter. Add in the onions and sauté, stirring often until softened, about 10 minutes, scraping up and mixing in any browned onions from the bottom of the pan.

Reduce heat to medium, stir in the salt and sugar; cook for another 35 minutes, stirring occasionally (every 5 minutes or so), until onions are caramelized and almost syrupy.

Use as desired on top of a burger or in a patty melt, in a grilled cheese sandwich, blended into a dip, with crostini, or stirred into Mac and cheese!