• Preheat the oven to 350°F. Grease and flour a 10-cup bundt pan. You can also use a nonstick spray for baking. Set aside.

Make the cake batter:

• In a large bowl, combine the baking mix and sugar. Using  a pastry blender, cut in the butter until the mixture is crumbly and resembles coarse meal. 
• In a large measuring cup, whisk together the milk, eggs, and vanilla. Add to the dry ingredients and stir until just combined. Mixture will resemble a thin, lumpy pancake batter in consistency. Set batter aside to rest for 10 minutes while you prepare the topping. 

Make the streusel:

• In a bowl, combine the brown sugar, baking mix, cinnamon and nuts. Using your fingertips, rub the butter into the brown sugar mixture until well combined and the mixture clumps together. 
• After the batter has rested for about 10 minutes, give the batter a final whisk and pour half of the batter into the prepared bundt pan, reserving the rest of the batter.
• Sprinkle half of the streusel over the batter in the pan. Top with the remaining cake batter, then sprinkle with the remaining streusel mixture.
• Bake for 45 minutes, or until the top is golden and a toothpick inserted comes out clean.
• Allow the cake to cool in the pan for at least 20-30 minutes before removing from the pan.