Use a mixer and beat together first 5 ingredients for a couple minutes until smooth.
In another bowl use a pastry blender or fork to make streusel by mixing brown sugar, flour, cinnamon, and butter until crumbly. Add nuts to streusel if using.
Sprinkle about 1/4 cup of the streusel mixture in the bottom on the greased bundt pan.
Then top with half of the cake batter.
Next, remaining streusel on top of the batter.
Use a knife to swirl the streusel mixture into the batter a bit.
Bake in a preheated 350 oven for 35 to 45 minutes or until a toothpick inserted comes out clean.