Preheat oven to 350 degrees. Line a muffin tin with paper liners or spray well with non stick cooking spray. Set aside.
In large bowl, whip oil, sugar, eggs, vanilla, sour cream and milk until well combined and light in color, 3 minutes or so. Fold in remaining ingredients until just combined.
In small bowl, mix cream cheese, sugar and flour together until smooth. Set aside.
Scoop 1 large spoonful of muffin batter into prepared muffin tins to be 1/3 way full. Drop small spoonfuls of cream cheese mixture into middle of muffin batter (should be about 1 1/2-2 teaspoons per muffin). Scoop another large spoonful of muffin batter and pour overtop cream cheese mixture. Muffin tins should be filled 2/3-3/4 way full.
Bake 20-25 minutes. Remove from oven and cool 10 minutes before removing from tins. Dust with powdered sugar if desired. Once cooled, store in air tight containers, ideally in the fridge.