Preheat & Prepare – Preheat your oven to 350°F. Grease and line an 8x8-inch baking pan with parchment paper.
Make the Crumb Topping – In a small bowl, mix the flour, brown sugar, cinnamon, and salt. Pour in the melted butter and stir until crumbs form. Gently fold in the mini chocolate chips. Set aside.
Mix Dry Ingredients – In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
Cream Butter & Sugar – In a large bowl, beat the softened butter and granulated sugar until light and fluffy. Add in eggs one at a time, mixing well after each. Stir in vanilla extract.
Combine Wet & Dry – Mix in the sour cream (or Greek yogurt) and half of the dry ingredients. Pour in the milk and then add the remaining dry ingredients, stirring until just combined.
Fold in Chocolate Chips – Gently mix in the chocolate chips to evenly distribute throughout the batter.
Assemble & Bake – Pour the batter into the prepared pan, spreading it evenly. Sprinkle the crumb topping over the top. Bake for 35-40 minutes, or until a toothpick inserted in the center comes out clean.
Cool & Enjoy – Let the cake cool in the pan for about 15 minutes before slicing. Serve warm or at room temperature!
