Preheat your oven to 375 degrees F. Prepare an 8x8 or 9x9 in baking pan by spraying it liberally with cooking spray. You want to make sure the coffee cake doesn't stick to the pan.
In a medium sized bowl mix together the flour, baking powder and salt with a whisk. Set this bowl aside.
In a large bowl (I would recommend using a stand mixer if you have one) add the 1/2 cup of butter (1 stick) and granulated sugar. Beat the butter and sugar for at least 2-3 minutes until creamy. Add your room temperature eggs one at a time to the butter. Beat until well combined.
Beat in your vanilla and the lemon zest from one lemon to the butter mixture.
Add the dry ingredients (flour, salt and baking powder) gradually into the butter mixure alternating with the milk. Beat on low speed until these ingredients are mixed together (make sure you don't over mix). Fold in the blueberries.
To make the strussel topping mix the brown sugar, flour, cinnamon, nutmeg and salt in a small/medium sized bowl. Cut the cold butter into small squares and mix the ingredients together with your hands. Don't over mix these ingredients because you want the cold butter to still have some texture in the mixture.
Pour your batter into the prepared pan. Spread out the batter to fill the whole pan. Sprinkle the topping on the batter.
Bake the coffee cake for 35-45 minutes. The coffee cake should be slightly brown and if you insert a toothpick it should come out clean. Let the coffee cake cool in the pan on a wire rack.