Preheat over to 350°F and line a 9x9-inch baking pan with parchment paper.
Cream together the butter and sugar in a mixing bowl.
Beat in the egg and vanilla. The mixture may be a bit lumpy, that’s okay.
Combine flour, baking powder, and salt in a separate bowl.
Slowly add buttermilk and flour mix, alternating between until incorporated in the butter mix.
Gently fold in the strawberries with a rubber spatula.
Pour the batter into the prepared baking pan.
In a mixing bowl, beat topping ingredients until fully combined.
Sprinkle the topping over the top of the batter and bake for 30 to 40 minutes until the top is golden brown and a toothpick comes clean from the center of the cake.
Allow the coffee cake to cool in the pan for about 1 hour before cutting. This gives the coffee cake time to finish setting up.