Preheat oven to 350°F. Coat a 6-inch round baking pan with nonstick spray. Line bottom with a round of parchment.

In a large bowl, whisk the brown sugar and eggs until pale and foamy, about 1 minute. Add oil, vanilla, cinnamon, nutmeg, salt, and whiskey and espresso powder, if using. Whisk until smooth and emulsified.

Add the flour, baking powder, and baking soda and whisk until well-combined and smooth.

Use a rubber spatula to fold in the apples and 1/2 of the nuts.

Pour the batter into the prepared pan and gently smooth the top. Tap the pan gently on the counter to release any air bubbles. Sprinkle the remaining nuts over the cake.

Bake until puffed and golden, and a tester comes out clean, 30 to 40 minutes. Cool for about 15 minutes. Runknife around the edge and carefully turn the cake out onto a cooling rack. Then invert it again so that its puffy side is up

Store the cake, wrapped tightly, at room temperature or in the fridge for up to two days.