Preheat the oven to 350°F (175°C). Grease a 9×9-inch pan and line with parchment if you want easy removal.

In a medium bowl, whisk together the flour, sugar, baking powder, baking soda, and salt. Set aside.

In a large bowl, cream the softened butter and egg until light and slightly fluffy using a handheld mixer for 1–2 minutes.

Stir in the cooled brewed coffee, buttermilk, and vanilla extract until combined.

Add the dry ingredients gradually and mix just until the batter is smooth.

Pour the batter into the prepared pan and smooth the top. Bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Let the cake cool in the pan on a rack for 15–20 minutes while you make the caramel.

In a saucepan over medium heat, combine the packed brown sugar, butter, and heavy cream.

Stir constantly until the mixture comes to a gentle simmer. Let it simmer for 3–4 minutes, stirring frequently.

Remove from heat and stir in the vanilla, a pinch of salt, and brewed coffee.

Pour the warm caramel evenly over the cooled cake.

Dust with powdered sugar if desired. Serve warm or at room temperature.