In a large skillet over medium heat, heat three tablespoons of olive oil and add the onions. Toss to coat evenly with oil and let cook. 

Add a pinch of salt and the brown sugar, then stir and cook until the onions are browned. (You can add a tablespoon or so of water if the skillet is a little dry.) Remove skillet from heat and let cool.

Preheat oven to 375°F, placing the rack in the top third of the oven. Generously spray a 9-inch springform pan with cooking spray and set aside.

Pour the remaining three tablespoons oil into a small bowl.

Arrange the potato slices in the 9-inch pan, starting at the outer edge and working your way to the center, overlapping the slices.

Brush with oil and sprinkle with a generous amount of salt and pepper. Layer a quarter of the onions.

Add another layer of potatoes, brush with oil and sprinkle with salt and pepper, and then top with the second quarter of onions and a third of the goat cheese. Repeat two more times. Top with a final layer of potatoes. 

With a spatula, press down firmly to compress. Brush the top with more oil and a final sprinkling of salt and pepper.

Bake uncovered for 80 to 90 minutes, until potatoes are tender, compressing it twice more while baking. Invert onto a serving plate and serve.