Preheat oven to 325 degrees. Grease and flour bundt pan or tube pan. (See Notes for additional pan details)
In a separate bowl combine the cake flour, baking powder and salt. Whisk at least 30 seconds to blend. Set aside.
In another bowl combine the sour cream, vanilla, oil and milk. Stir and set aside.
In the bowl of your mixer, add the butter and beat on low to medium speed until smooth. Slowly add the white and brown sugar, mixing on medium speed until the mixture is lighter in color and fluffy, approximately 3 to 5 minutes ( a bit longer if using a hand mixer).
Add the eggs one at a time, mixing after each egg until the yellow of the yolk is blended in.
With the mixer on low, add the dry ingredients alternately with the wet ingredients, beginning and ending with the dry ingredients. (We did three additions of the dry ingredients, alternating with two additions of wet.) Stop & scrape down sides of bowl with rubber spatula as needed (once or twice).Mix just until combined.
Once the batter is mixed, using a spatula fold in the toffee bits and the chopped pecans. The cake batter is thick, this will help to keep the nuts and toffee bits from sinking to the bottom of the pan.
Scoop batter into the prepared bundt pan. Smooth the top with the back of a spoon. Bake for 45-50 minutes (adjust time as needed). The cake is done when a toothpick inserted into the center pulls out clean or with just a few crumbs attached. Let the cake cool in the pan on a wire rack for 10 minutes before turning out.
This recipe makes about 8 cups of batter