Preheat the oven to 400°F (200°C). Line a 9x13-inch/23x30 cm baking pan with parchment paper.
In a mixing bowl, stir together the cream cheese, cornstarch, and powdered sugar until smooth. Transfer the filling to a piping bag.
Place one sheet of phyllo on a clean work surface. Brush it with melted butter, then layer a second sheet on top and brush again. Fold the double layer lengthwise to form a long strip.
Spread a thin layer of jam across the folded phyllo. Pipe a line of cheese filling along one long edge. Roll up tightly, then tuck in the ends to seal. Place seam-side down in the prepared pan.
Repeat with the remaining sheets and filling. Arrange the rolls snugly in the pan. Cut each roll in half crosswise. Brush the tops with more melted butter.
Bake for 18 to 22 minutes, until golden and crisp. Remove from the oven, dust with powdered sugar, and serve warm.