Preheat oven to 350 °F (177 °C). Line muffin tins with baking cups, set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together butter and brown sugar until creamy and fluffy. Add in the bananas, eggs, and vanilla extract. Beat well until incorporated.
1/2 cup unsalted butter, 2/3 cup packed dark brown sugar, 4 medium ripe bananas, 2 large eggs, 1 teaspoon vanilla extract
In a medium bowl, whisk together flour, baking soda, cinnamon, and salt.
2 cups all purpose flour, 1 teaspoon baking soda, 1 teaspoon ground cinnamon, 1/4 teaspoon salt
Slowly add in the dry ingredients until just combined. Spoon batter evenly into prepared muffin tins.
In a small bowl, combine all streusel ingredients except the toffee bits. Mix well then stir in toffee bits.
1 cup all purpose flour, 1/2 cup dark brown sugar, 1/2 cup unsalted butter, 1 cup toffee bits
Generously spoon streusel mixture all over the tops of the muffin batter.
Bake for 18-25 minutes or until light golden brown. Let stand for 5 minutes before removing muffins from pan. Let cool completely on a wire rack.