Preheat the oven: Preheat your oven to 190°C (375°F).
Prepare the filling: Sauté the chopped onions and garlic in a pan until translucent. Add the sliced mushrooms and cook until softened. Season with salt and black pepper. Stir in the chopped spinach and cream and cook for a few more minutes until the mixture is well blended and creamy.

Roll out the dough: Roll out the puff pastry on a lightly floured surface into a rectangular shape.
Add the filling: Spread the mushroom and spinach mixture evenly over the puff pastry, leaving a small border around the edges. Sprinkle with melted cheddar, shredded cheese, and grated Parmesan cheese.
Roll and slice: Carefully roll the dough into a log, starting at one of the longest sides. Once rolled, cut the log into equal pieces, about 1 inch thick.
Bake: Place the slices on a baking sheet lined with parchment paper. Bake in the preheated oven for 20 to 25 minutes, or until the crust is golden brown and puffed up.
Prepare the sauce: Meanwhile, prepare the sauce by whisking the cream cheese, diced tomatoes, shredded cheddar, and sour cream until smooth.