In a small bowl, Add in brown sugar and cinnamon. Stir until the cinnamon is thoroughly mixed into the sugar.
Add in the flour and stir.
Cube the butter and place into the bowl. Using a fork, cut the butter into the flour/sugar mixture until there are no more large chunks. It will start to look like wet sand.
Place in the freezer for about 30 minutes to an hour.
Muffin
Preheat oven to 375. Line a large muffin pan with liners.
In a large bowl, add the sugars, cinnamon, and pumpkin pie spice. Whisk until the spices are incorporated.
Add in the pumpkin and oil. Whisk together.
Add in the eggs, vanilla, and milk. Give it a whisk until everything is combined.
In a separate bowl, sift together cake flour, baking soda, baking powder, and salt.
Add the dry ingredients into the wet ingredients and whisk until combined.
Add in toffee bits and walnuts. Stir.
Pour into the muffin liners until two-thirds full. Place a few chunks of the streusel on the top of the muffins and push them down into the center.
Place into the oven at 375 for 15 minutes and then reduce the heat to 350 for 10 minutes. Check to see if the muffins are done by placing a tooth pick close to the center. If it comes out clean, they're done!