1Toast 0.75 cup of walnuts on medium-low heat in a skillet.
2Add 0.5 stick of butter, 1 tablespoon of vanilla, and 1 tablespoon of light brown sugar to the walnuts and simmer on low heat for 3-5 minutes.
3Remove from heat to cool.
4In a bowl, combine 0.5 cup of flour, 0.5 tablespoon of ground cinnamon, 0.5 cup of light brown sugar, 0.25 cup of white sugar, and 1 teaspoon of salt.
5Add 0.5 stick of cubed cold butter to the dry ingredients and cut the butter into the mixture with a fork or pastry cutter.
6Set aside.
7Add the buttered walnuts to a yellow cake mix.
8Omit the 1/4 cup of oil from the cake mix instructions.
9Mix until the ingredients are just combined.
10Add the batter to a prepared cake pan.
11Sprinkle the streusel evenly over the batter.
12Bake at 340°F for 45-50 minutes.
13Let the cake cool for at least 10 minutes before releasing it from the cake pan.