Do not preheat the oven. Liberally butter and flour a tube pan. Set aside. (See Cook's note)
In the bowl of a stand mixer cream together the butter, shortening, vanilla, brown and granulated sugars. Beat for 2 minutes or until creamy and light beige in color..
Add the eggs one at a time beating well after each addition stopping to scrap the sides of the bowl as needed.
Sift together the flour, baking powder and salt. Lower the speed of the mixer and add to the creamed mixture alternately with the buttermilk. After all has been added increase the speed of the mixer to medium and beat until fully combined around 45-60 seconds.
By hand mix in 1 ½ cup pecans and toffee bits. Spread into the prepared pan.
Place the cake into a cold oven. Bake at 325F for 1hr 30min to 1hr 45min or until a long skewer inserted into the center comes back clean.
Cool in the pan on a cooling rack for 30 minutes then turn onto the rack to cool completely.
To make the glaze. In a deep microwave safe bowl melt the butter in the microwave. Whisk the brown sugar and heavy cream into the melted butter then return to the microwave..
Cook on high for 2 minutes. Remove from the microwave and stir in the vanilla and ¼ cup pecans. Allow to cool slightly then drizzle over the cake.
I baked this cake in a cake pan similar in shape to a bundt pan but, it's slightly larger and holds more batter. I recommend you bake this cake in a 10-inch tube pan. If using a standard size bundt pan, place onto a sheet pan to bake to catch drips.