Preheat the oven to 400°F (200°C). Melt 1 tbsp butter in a small skillet over medium heat, add 1 cup spinach and 1/2 cup roasted red pepper, and cook for 2 minutes until the spinach wilts. Transfer to a plate and cool for 5 minutes.

Whisk 4 eggs with 3 tbsp heavy cream, 1/2 tsp kosher salt, 1/4 tsp black pepper, and 1/4 tsp garlic powder until combined. Stir in the cooled vegetables and 3/4 cup shredded cheese.

Cut each puff pastry sheet into 4 squares (8 total) and press each into a cup of a standard muffin tin, letting the corners flare over the edge.

Beat the remaining 2 eggs and brush the pastry edges with the egg wash. Divide the filling evenly among the 8 cups, filling each about three-quarters full.

Bake at 400°F (200°C) for 22 to 25 minutes until the pastry is deep golden brown and the filling is fully set.

Run a knife around each soufflé, lift onto a serving plate, and finish with a pinch of flaky salt and a grind of black pepper before serving.