Preheat the oven to 350°F. Line a baking sheet with parchment paper or a silicone mat.

Keep the thawed phyllo covered with a clean, slightly damp kitchen towel while you work so it does not dry out.

Stack all 9 phyllo sheets and cut them into rectangles about 3 × 5 inches.

Divide the cut rectangles into three stacks of 3 sheets each and place the stacks on the prepared baking sheet, spaced apart.

Brush melted unsalted butter between each sheet in every stack (place a sheet, brush butter, place next sheet, brush, place third sheet, brush). Use all 4 tablespoons of melted butter across the stacks.

Cover the stacks with another piece of parchment or a silicone mat and place a second baking sheet on top to weigh them down.

Bake for 10–15 minutes, until the phyllo is golden and crisp. Remove the top tray and covering, then transfer the baked phyllo to a rack and let cool completely.

While the phyllo cools, chill a mixing bowl if possible, then beat 1 cup chilled heavy cream with 2 tablespoons powdered sugar until soft peaks form. Transfer the whipped cream to a piping bag or keep a spoon handy for assembly.

Assemble each Napoleon: place one baked phyllo rectangle on a plate, pipe or spread whipped cream, top with a second phyllo, add more whipped cream, and finish with the third phyllo (phyllo → whipped cream → phyllo → whipped cream → phyllo).

Dust the assembled Napoleons with 1/3 cup powdered sugar (or more, to taste) and arrange the 4–8 hulled, sliced strawberries (or other berries of choice) on top. Serve immediately.