Begin by preparing the onions. Heat the vegetable oil in a large skillet over medium heat for 2 minutes.
Add the onions, salt, and pepper and cook, stirring occasionally, for 2 minutes until onions are soft.
Add the sugar and reduce the heat to medium-low. Cook the onions, stirring frequently, for 10 minutes.
Add the balsamic vinegar and reduce the heat to low. Continue cooking the onions, stirring occasionally, for 1 hour until they are very soft and dry. Set aside.
Preheat oven to 500ºF.
Roll out the prepared pizza dough on a lightly floured surface until it is roughly ¼-inch thick.
Invert a cookie sheet and sprinkle it liberally with cornmeal. Transfer dough to cornmeal-dusted sheet tray. (See Notes.)
Combine the olive oil and garlic and brush it over the dough, leaving a ½-inch border along the edges.
Top it with half of the shredded gruyere, then sprinkle on the prepared balsamic onions.
top with the remaining cheese.
Bake pizza for 10 to 12 minutes, rotating half-way through, until crust is fully baked and golden brown.
Garnish with chopped chives, slice and serve.
You can use a pizza stone in place of the inverted cookie sheet.
Oven temperatures and positions may vary, so make sure you are baking your pizza on the middle rack and check it frequently.