Preheat and Prep: Preheat your oven to 360°F (180°C) and grease an 8x8-inch cake pan with butter.
Prepare the Milk: In a small bowl, mix the lemon juice or vinegar with the milk. Stir and set aside.
Combine Dry Ingredients: In a large bowl, sift together the flour, salt, baking powder, and baking soda. Set aside.
Cream Butter and Sugar: Using a stand mixer or hand mixer, cream together the butter and sugar until light and fluffy. Add vanilla extract and mix. This takes me 4-5 minutes usually. Remember to scrape the sides with a rubber spatula every once in a while.
Add Eggs: Add eggs, one at a time, mixing until just combined after each addition.
Alternate Mixing: Alternate adding the flour mixture and milk mixture to the butter mixture, beginning and ending with the flour mixture. Mix until just combined.
Make the Filling: In a small bowl, mix together the filling ingredients until well combined.
Prepare the Streusel Topping: In another bowl, combine all streusel ingredients until you get coarse crumbs
Layer and Bake: Spoon half of the batter into the prepared pan and spread evenly. Sprinkle the filling mixture over the batter. Top with the remaining batter and spread evenly. Finally, sprinkle the streusel topping over the top of the batter.
Bake: Bake for 45 minutes, or until a toothpick inserted into the center comes out clean.