Preheat oven to 350°F (175°C). Grease and lightly flour a 23x33 cm baking dish.
In a large bowl, combine yellow cake mix and instant butterscotch pudding mix.
Add eggs, whole milk, vegetable oil, and vanilla extract. Beat with an electric mixer on medium speed for 2 minutes until smooth.
Pour batter into prepared baking dish and smooth the surface.
Bake for 28 to 32 minutes or until a toothpick inserted in the center comes out clean. Cool in pan 15 minutes.
In a small saucepan over medium-low heat, melt butterscotch chips with heavy cream and butter, stirring until smooth and glossy.
Remove glaze from heat and let thicken for 3 minutes.
While cake is warm, poke holes across the surface with a fork or skewer.
Pour warm glaze evenly over cake, spreading with an offset spatula.
Top with toffee bits, chopped butterscotch chips, and crushed granola. Press gently into glaze.
Let cake rest for at least 30 minutes to set before serving.