Preheat your oven to 350°F (180°C) and grease a 9x13-inch baking dish.

In a large mixing bowl, cream the softened butter and granulated sugar until light and fluffy.

Add the eggs and vanilla extract, and beat until combined.

Mix in the sour cream until the batter is smooth.

In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, stirring until the batter is well combined.

In a small bowl, mix together the ingredients for the streusel until crumbly.

Pour half of the batter into the prepared baking dish and spread it evenly.

Sprinkle half of the streusel over the batter.

Pour the remaining batter over the streusel and spread it evenly.

Sprinkle the remaining streusel over the top of the batter.

Bake the coffee cake for 40-45 minutes, or until a toothpick inserted in the center comes out clean.

Allow the cake to cool for at least 10 minutes before slicing and serving.