Soften butter for the cake in microwave for 15 seconds. Leave the butter for the streusel in the refrigerator.
Make the Cake
In a small bowl, cream softened butter and sugar together thoroughly. Stir in the other wet ingredients.
Mix up the dry ingredients in a larger bowl,using a wisk to thoroughly combine.
Add the small bowl (wet) mixture to the large bowl (dry mixture) and hand stir until just combined.
Pour this mixture into the parchment lined pan, spreading to the corners evenly with a spatula. Hold back about ½ of the mixture.
Make the Streusel
Place the streusel ingredients into a bowl, stir together roughly with a fork and then use two knives to make criss-cross cuts through the mixture. You basically want a crumbly cinnamony lumpy mixture.
Sprinkle ½ the streusel over the batter in the pan, putting it on heavier on the edges. Then dollop on the remaining batter in sporadic dots so some of the batter surface has plain batter and other areas have clumps of streusel showing - this gives the cake a pull-apart effect after baking.
Bake at 375F for 35-45 minutes or until a test comes out clean. Remove from oven and let cool before slicing.