In a light-colored saucepan, melt the butter over medium heat. Stir often until it foams, then turns golden with brown specks on the bottom, about 5–7 minutes. Immediately whisk in the espresso powder until fully dissolved. Set aside to cool slightly.

In a small bowl, mix together the pumpkin puree, sugar, pumpkin pie spice, and a pinch of salt until smooth. Set aside.

Set your oven to 350°F (177°C) so it’s ready when your batter is done. Line an 8x8-inch baking pan with parchment paper, leaving a bit of overhang for easy removal later.

In a large mixing bowl, whisk the cooled brown butter mixture with the brown sugar and granulated sugar until smooth. Add the egg, egg yolks, and vanilla extract. Whisk until the batter looks glossy and thick.

Fold about 3/4 of the pumpkin swirl mixture into the wet batter, leaving streaks for a marbled effect.

Sift in the flour, cinnamon, pumpkin pie spice, clove, baking powder, cornstarch, and salt. Gently fold until just combined. Avoid overmixing so the bars stay tender.

Pour the batter into the prepared baking pan and smooth the top with a spatula. Dollop the remaining pumpkin mixture on top and use a butter knife to gently swirl it into the batter.

Bake for 26–30 minutes, or until the edges are set and the center looks slightly underbaked—it will finish setting as it cools.

Allow the bars to cool completely in the pan before lifting them out with the parchment paper. Slice into squares and enjoy!