Cookbooks are notoriously unreliable about caramelizing onions, the process takes a half hour or more in spite of what any book says.
Skip the baking soda, that destroys the nutrition,
Use a HEAVY saute pan.
Any vegetable oil will do, use what you have on hand, mixed olive oil and butter does add a nice flavor. Use enough oil to coat the entire pan.
Heat the pan with oil in it before adding onions.
Start with a medium to low heat so the onions don't burn.
Add the onions and stir very frequently.
IF you have a lid for the pan cover it and let the onions steam until they wilt.
Continue cooking and stirring and the onions will brown.
Keep cooking and stirring until you have the color you want.
Don't try to rush it by raising the heat, all you get is burnt bitter onions
(At home I sometimes microwave the onions to soften them, this saves a lot of time)