Preheat the oven to 350°F (175°C). Grease and flour a 9x9 inch baking pan.

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

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

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

Gradually add the dry ingredients to the wet mixture, alternating with the sourdough discard until just combined.

In a separate bowl, combine the flour, brown sugar, and cinnamon.

Cut in the cold butter using a fork or pastry cutter until the mixture resembles coarse crumbs.

Pour the cake batter into the prepared baking pan and spread evenly.

Sprinkle the streusel topping evenly over the batter.

Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.

Allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.