When the pizza dough is starting the final hour of second rise (or after removing dough from the refrigerator after overnight rise), prepare the caramelized onions.
Add olive oil, onions, and a small pinch of salt to large frying pan. Sauté over medium heat for about 4 minutes until onions become soft and translucent, stirring frequently. Turn heat down to medium-low and continue cooking onions for 20 – 35 minutes more, stirring frequently, adding spoonfuls of water as needed when onions seem dry. Lower the heat if onions start to burn. Continue cooking and stirring until you reach your desired level of caramelization. Add the balsamic vinegar and stir well to combine. Set about 2 generous tablespoons of onions aside for the pizza and store any remainders in the refrigerator for another use.
Prepare the other toppings. Cut the prosciutto slices into thin strips, then cut into smaller lengths if you like. Shred the mozzarella and crumble the blue cheese.
Place baking steel on oven rack in lower half of the oven. Preheat the oven and baking steel to 530 - 550 degrees F as your oven allows. Or follow manufacturer guidelines regarding recommended cooking temperatures for your baking steel or baking stone.
When your dough is ready, shape one dough ball into 10-to-11-inch round. Shape directly on a wooden pizza peel or board, using flour on the surface as needed so dough does not stick. Once shaped, give the peel a shake to ensure pizza is not sticking, adding some flour underneath the round if there are any sticky spots.
Spoon the fig spread onto center of dough round. Use the bottom of a spoon to gently spread the fig spread into thin layer without tearing the dough, leaving about an inch at the outer edge.
Scatter the shredded mozzarella over the fig spread. Scatter about 2 Tbsp of the caramelized onions over the cheese. Add the strips of prosciutto. Finally, add the blue cheese crumbles.
Transfer pizza onto hot baking steel. Cook for about 7-8 minutes, until edge of pizza is puffed and lightly browned and cheese is starting to brown in spots. Remove pizza from oven. Cool for 10 minutes. Slice in triangles (like a pie) and serve.