Preheat your oven to 350°F (175°C). Grease an 8-inch square pan or line it with parchment paper, greasing the parchment as well.

In a medium saucepan, mix together granulated sugar, pumpkin purée, vegetable oil, melted butter, pumpkin pie spice, and salt. Heat over medium, stirring until combined, about 3 to 5 minutes.

Remove from heat and let cool for 10 to 15 minutes, stirring occasionally until warm but not hot.

Crack in a large egg and stir to combine well.

Add the all-purpose flour and baking powder, stirring until completely smooth without streaks of flour.

Pour the batter into the prepared pan and smooth it into an even layer.

Bake in the preheated oven for 32 to 36 minutes, until set, and a toothpick comes out clean.

Let the bars cool in the pan for about 15 minutes, then transfer them to a wire rack to cool completely.

In a microwave-safe bowl, whisk together milk, espresso powder, and a pinch of salt. Microwave in 10-second intervals, stirring until espresso powder dissolves.

Stir in confectioners' sugar to form a smooth glaze and pour over cooled bars.