Pre heat the oven to 400F.
Cut the puff pastry into 4 squares and place on a baking tray lined with parchment paper or a Silpat. With a butter knife, score a 1 inch rim inside the square, cutting about half way through the pastry and bake for 10-12 minutes until puffed up and lightly golden brown.
Lower oven temperature to 325F
If using, fry the bacon in a pan until crispy, drain and set aside.
FOR FRESH SPINACH: Bring 1/2 inch water to a boil in a large skillet, then add half of spinach and cook, turning with tongs, until wilted, about 30 seconds. Add remaining spinach and wilt in the same way, then cook, covered, over moderately high heat until spinach is tender, about 1 to 2 minutes. Drain in a colander and cool under cold running water. Gently squeeze handfuls of spinach to remove as much liquid as possible, then coarsely chop. FOR FROZEN SPINACH: Defrost in microwave, run under cool water and squeeze as much liquid out as possible, then coarsely chop.
Melt butter in a skillet over medium-low heat. Cook onion and garlic until softened, 4 to 5 minutes. Add the spinach back in and stir in enough cream to coat the spinach lightly (frozen will soak up a bit more because it’s drier), season with salt and pepper. Simmer until the cream reduces and there’s not much liquid left (2-3 minutes). Remove skillet from heat.
Remove pastry from the oven and, using a spoon, push down the inner cavity carefully so that you create a raised rim with the sides of the pastry (be careful of the steam the hot pastry will let out). Arrange the spinach on the bottom and around the sides leaving a slight well in the center. Top with the grated cheese, and if using, place the crumbled bacon around the edge. Break an egg into a small ramekin and gently slide it into the middle of the well, repeating with each tart. Return to the oven and bake for a further 10 - 15 minutes until the eggs are just set but yolks are still slightly runny.
FOR ROASTED TOMATOES: Place tomatoes on a baking tray and drizzle lightly with olive oil. Sprinkle with course kosher salt and pepper and roast at 400F for 10-12 minutes, until the skin just blisters and splits. Set aside.