In small bowl, combine 1/3 cup flour, 1/3 cup brown sugar and 1.5 tsp. cinnamon.
Add 1.5 Tbs. butter and crumble together with a fork or fingers to make fine crumbs.
Set this streusel topping aside.
Stir the flour, salt and baking powder in a large bowl.
With an electric mixer, cream butter and sugar. Add the eggs, vanilla and milk and mix until well blended.
Stir wet ingredients into dry ingredients with a spoon. Stir gently, just until combined.
Spoon some batter into the bottom of 12 greased muffin cups. You’ll use about half of the batter for this step.
Generously sprinkle streusel onto each muffin. Use more than half for this. It will look like too much, but be generous with it.
Dollop the remaining batter onto tops of muffins. It may not be enough to cover the streusel, but the batter will spread out when baking.
Sprinkle remaining streusel on tops of each muffin.
Bake at 400 degrees for 20-25 minutes, until a toothpick comes out clean.