Preheat your oven to 400°F (200°C). Toss the cubed butternut squash with olive oil and spread it in a single layer on a baking sheet. Slice about ½ inch off the top of each garlic head so all cloves are exposed. Drizzle a little olive oil over the garlic heads and place them, cut-side down, on the same baking sheet with the squash. Roast for 20 minutes, then check the squash. If it is soft, remove the squash to a bowl and set aside. Leave the garlic in the oven for about 10 minutes more, until it is soft and fragrant.
Once the roasted garlic has cooled enough to handle, gently squeeze the cloves out of their skins. Mash 10 of the roasted garlic cloves with a fork in a small bowl to form a paste and leave the remaining roasted garlic cloves whole. These will be used later for the sauce and as pizza topping.
While the squash and garlic are roasting, heat the butter and olive oil in a large pan over medium heat. Add the thinly sliced onion and cook, stirring occasionally, until translucent. Reduce the heat to medium-low, stir in the maple syrup, and cook until the onions are light golden brown and deeply caramelized. This usually takes about 15-20 minutes in total. I like to let the onions caramelize slowly to bring out their natural sweetness.
Melt the butter in a frying pan or small pot over medium heat. Add the flour and whisk until combined, cooking for about 1 minute to eliminate any raw flour taste. Gradually whisk in the milk and bring the mixture to a boil, whisking constantly, until thickened. Remove from heat and stir in the mashed roasted garlic (from Step 2). Season with salt and pepper to taste. For extra depth, I sometimes add a pinch of nutmeg to the sauce.
On a lightly floured surface, shape both pizza dough balls into desired shapes and thickness. Spread the prepared white sauce (from Step 4) evenly over each dough base. Top with the caramelized onion topping (from Step 3), roasted butternut squash (from Step 1), whole roasted garlic cloves (from Step 2), baby spinach leaves, chunks of goat cheese, and sprinkle with minced fresh rosemary. Try to distribute the toppings evenly for the best flavor in each bite.
Bake each assembled pizza one at a time in the preheated 400°F (200°C) oven for 12-15 minutes, or until the crust is golden and the cheese is bubbling and slightly browned. Allow the pizzas to cool for a couple of minutes before slicing and serving. For a crispier crust, I sometimes bake the pizza directly on a preheated pizza stone.