A soft and juicy Blueberry and Lime cake topped with the most amazing crunchy crumb topping. The perfect zesty and tender cake to enjoy with a cup of coffee!
Preheat the oven to 180C/350F and spray an 8x8 inch square pan with cooking spray. Place a strip of grease proof paper along the middle overhanging the edge of the pan to make it easier to lift the cake out.
Make the crumb topping: Place butter, light brown sugar, oats and 1/3 cup plain flour into a small bowl and rub between your fingers until you have a crumbly mixture that resembles coarse breadcrumbs. Some larger lumps of butter are fine.
NOTE: You may need extra flour; up to 1/2 cup. It will depend how warm your hands are! You want a mixture that isn't sticky, but holds itself in lumps to create a great, crunchy crumb top! My fiancé made the crumb topping and his hands are so warm I needed the extra flour! (I should have made it myself, I have freezing hands!!!)
Leave crumb topping to one side, whilst you make the cake: Place butter, sugar and lime zest into a large bowl, or the bowl of your stand mixer and beat until light and fluffy; around 2 minutes on medium-high speed.
Add in the vanilla extract and eggs, scraping down the sides as necessary, and beat until well incorporated and smooth; around 1 minute on med-high speed.
Place the flour, baking powder, salt and blueberries into a medium sized bowl and mix until all the blueberries are coated in flour.
Tip the flour mixture into your egg mixture and mix on low until the mixture begins to come together, then add in the sour cream and continue mixing until everything is well combined and there are no lumps of flour. Be sure to keep the speed low, so you don't mash the blueberries up.
Tip the mixture into your prepared pan and smooth into an even layer with the back of a spoon/spatula.
Sprinkle the crumb topping all over the top of the cake, then place in the oven for 35-45 minutes until risen, the top is golden and an inserted skewer into the centre comes out clean.
Leave to cool in the pan completely, before lifting out onto a cutting board and slicing into 9-12 slices. Blueberry and Lime Coffee Cake will keep in an airtight container, at room temperature, for 4 days.
*I normally always use butter in recipes, however, last year by chance I ended up using a light margarine spread for a crumb topping and it made the best crumb topping ever, so now I always use it!!