To prepare the cake, beat the butter and sugar in a large bowl till the mixture becomes light and fluffy.
1/2 Cup Unsalted Butter, 3/4 Cup White Sugar
Add curd, sour cream, milk and vanilla essence to the bowl and blend them together.
1/2 Cup Sour Cream, 1/2 Cup Milk, 1/2 Cup Plain Curd, 1/4 Teaspoon Vanilla Extract
Separately mix all-purpose flour, baking soda, baking powder and salt.
1.5 Cups All Purpose Flour, 1 Teaspoon Baking Soda, 3/4 Teaspoon Baking Powder, 1/4 Teaspoon Salt
Add the dry ingredients to the wet mixture by the spoonful, slowly blending till all the mixture is incorporated.
Transfer the batter to a greased baking tray for making a cake or in a muffin tray for making muffins. Sprinkle the prepared topping evenly over the batter.
Bake the cake/muffins in a preheated oven at 180 C or 350 F for around 40 minutes. The topping will be crisp and golden brown in color.
Crumb Cake is ready. Let it cool completely on a wire rack before serving.