Preheat oven to 325. F.
Generously grease and lightly flour bundt pan. Set aside.
In a large bowl, cream together butter and shortening.
Mix in brown sugar and white sugar.
Add eggs, one at a time, beating well after each egg.
Fold in vanilla extract. Set aside.
In a medium bowl, whisk together flour, baking powder and salt.
Gradually add dry mixture into the wet mixture while alternating with the buttermilk and heavy cream.
Mix well until combined being sure to scrape down the sides of the bowl.
Fold in toffee pieces. (Can also add in some pecan pieces if desired)
Pour batter evenly into prepared bundt pan.
Shake the pan back and forth and up and down to even out batter and release air bubbles.
Bake on the middle rack for 1 hour and 10 minutes.
Remove from oven and let cake sit in pan for 10-15 minutes before removing and placing on a cooling rack to finish cooling.
When cake is completely cooled start making the caramel frosting.
In a large saucepan over medium-low heat, stir together sweetened condensed milk and brown sugar.
Keep stirring until bubbles begin to gently break on the surface.
Reduce heat if needed, do not let the mixture boil or simmer too rapidly to prevent burning.
Continue cooking for about 5 minutes until mixture thickens, stirring constantly.
Remove from heat and stir in butter and vanilla.
Stir vigorously until butter is combined.
Sauce will begin to thicken up even more as it cools.
Pour the hot caramel sauce over the cooled cake. (I always have sauce left over. Goes great on ice cream!)
Garnish the cake with pecan pieces and toffee pieces if desired (highly recommended)
Let cake sit until frosting begins to harden.
Slice and serve, add vanilla ice cream to take it over the top!