Heat the oven to 350°F and grease and flour a 9x13-inch baking dish.

Whisk the flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large bowl.

In a medium bowl, whisk the eggs, buttermilk, oil, and vanilla until combined.

Add the egg mixture to the flour mixture and beat with a hand mixer on medium speed for 2 minutes.

Stir in the hot coffee until the batter is smooth, then pour the thin batter into the prepared dish.

Bake for 32 to 38 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.

Cool the cake completely in the dish, about 2 hours.

Toast the pecans in a dry skillet over medium heat for 3 to 5 minutes, stirring often, until fragrant; transfer to a plate.

Put the chocolate chips in a heatproof bowl and warm 1/2 cup of the heavy cream in a small saucepan until steaming; pour it over the chips, wait 2 minutes, then stir until smooth.

Spread the chocolate mixture over the cooled cake and let it set for 15 minutes.

Melt the caramels with the remaining 1/2 cup heavy cream in a small saucepan over low heat, stirring often, until smooth, about 5 to 8 minutes; stir in the toasted pecans and spoon the mixture over the cake.

Let the cake stand for 20 minutes before slicing.