Preparation: Begin by setting your oven to preheat at a temperature of 350°F (175°C).

Crust Formation: In a sizeable mixing bowl, amalgamate the cake mix with one of the eggs and the specified amount of butter. Utilize a fork to integrate until the mixture reaches a crumbly texture. Firmly press this mixture onto the base of a 9x13 inch baking pan, which has been previously greased for ease of release.

Toffee-Pecan Mixture: In a separate bowl, combine the condensed milk, the second egg, and a splash of vanilla extract. Ensure these ingredients are blended seamlessly. Subsequently, fold in the toffee bits and chopped pecans, ensuring even distribution. Pour this luscious mixture over the previously prepared crust.

Baking: Position the pan in the preheated oven and allow it to bake for approximately 30 minutes. You'll notice the edges adopting a golden-brown hue. While the center might retain a slight jiggle, ensure you refrain from overbaking.

Cooling and Serving: Once baked to perfection, remove the pan from the oven and allow the bars to cool thoroughly. Upon reaching room temperature, segment them into individual bars and serve.