Preheat oven to 350 F.
Spray an 8 by 8 baking pan and set aside.
In a large bowl whisk together the milk, vinegar, vanilla, and oil. Set aside. (the vinegar and milk sitting together will make a buttermilk, skip this if using buttermilk)
In a small bowl, stir together the ingredients for the streusel...until crumbly.
After the milk mixture has set for about 10 minutes, add the rest of the ingredients (flour, baking powder, salt, cinnamon and sugar). Stir just until mixed.
Pour batter into the baking pan.
Drop the streusel into the pan by the spoonful and use a knife to drag it around, a bit, in swirls. Or, spread it on the top of the batter. (really, how you do your streusel is a personal preference :). Some people even double the streusel and do both the swirl and top)
Bake for between 35-45 minutes, checking after 35. It is done when a knife inserted comes out clean. Serve warm, with butter.