Preheat oven to 350°F and grease three 9-inch round cake pans.
In a large bowl, whisk together flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt.
In another bowl, beat eggs, then add buttermilk, coffee, oil, and vanilla extract.
Gradually combine wet and dry ingredients until smooth.
Divide batter evenly among prepared pans and bake for 25-30 minutes.
For caramel, heat brown sugar, 1/2 cup heavy cream, butter, and salt in saucepan until thickened.
Whip remaining cream to soft peaks.
Layer cakes with caramel and whipped cream, then top with toffee bits and pecans.