Cream butter and sugar in an electric mixer.
Add egg and beat until fluffy.
Add remaining ingredients, and mix only until well combined.
Place batter in a greased 9x9" pan.
In a separate bowl, stir streusel ingredients together with a fork. Sprinkle over cake batter.
Bake at 350* for 22-25 min till done (using toothpick test).
Serve with fresh strawberries, and milk or whipped cream.