Make the dip: Preheat oven to 350 degrees. Slice off the top fifth of the head of unpeeled garlic. Add a drop of olive oil. Replace the top. Wrap with parchment paper and then aluminum foil. Bake for 1 hour. Discard foil and parchment.Take the top off of the garlic and squeeze the softened garlic out of the skins into the bowl of a food processor fitted with the metal blade. Add remaining ingredients and process until smooth and creamy. Can be made a day ahead and kept covered and refrigerated.Raise oven temperature to 400 degrees. Line a large baking sheet with unbleached parchment paper. Place the defrosted artichoke hearts on the prepared baking sheet and drizzle with olive oil. Toss to coat and sprinkle with salt and pepper. Roast until golden and crisp on the edges, about 20 minutes. Set aside to cool. Chop coarsely.Meanwhile, heat 1 Tablespoon olive oil in a large skillet over medium heat. Add the chopped onion and sauté until tender, about 6-8 minutes. Lower the heat to medium-low and continue to sauté the onions, stirring occasionally, until the onions are lightly caramelized, another 10-15 minutes.Transfer the onions to a bowl and wipe out the skillet. Place it back over medium and add 2 Tablespoons olive oil. Add the garlic and crushed red pepper flakes and sauté until fragrant and the garlic is just starting to turn golden, about 30-60 seconds. Add the cherry tomatoes plus a big pinch of salt and pepper and sauté until the cherry tomatoes have slightly lost their shape, about 5-7 minutes. Set Aside.Preheat the broiler.Layer the dip. Spread the white bean dip on the bottom of an 8 x 8-inch baking dish or 9-inch pie plate. A cast iron skillet works, too. Then top with the pesto, then the roasted artichokes, then the roasted red peppers, then the onions, and then the tomatoes. Arrange the mozzarella, if using, on top and broil 6 inches from the heating element until the cheese is melted and browned, about 2-3 minutes. If you don’t use the mozzarella, you can still broil the dip a little to help warm it through and meld the flavors. Serve with toasted baguette slices and/or endive leaves.