Preheat the oven to 350°F and grease an 8x8 square metal pan (or note longer baking time for a glass dish).

Use five bowls: two small, two medium, and one large.

For the streusel topping: Melt butter, combine with flour, brown sugar, cinnamon, and salt. Set aside.

Optional cinnamon and brown sugar layer: Mix 1/3 cup brown sugar and 1 tsp cinnamon in a small bowl.

Coffee Cake: In one medium bowl, combine oil, egg, vanilla, and milk. In a large bowl, combine flour, granulated sugar, baking powder, and salt.

Pour the wet mix (from Step 5) into the dry mix (from Step 6) and stir.

Spread half of the batter in the pan.

Sprinkle the cinnamon and brown sugar mix from Step 4 (optional).

Pour the remaining batter and spread it.

Sprinkle the streusel topping from Step 3.

Bake (18-20 mins for metal, 30-35 mins for glass). Let it cool.