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1
Preheat oven to 350 F and grease and line an 8 x 8 inch square pan.
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2
Make the crumb topping first: Place butter, flour and sugar into a medium sized bowl and rub between your fingers until you have a coarse breadcrumb texture. Some larger lumps are fine. Leave to one side.
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3
For the cake: Place butter, sugar and lemon zest into a large bowl or the bowl of your stand mixer and beat until light and fluffy, about 2 minutes on medium-high speed. Add in the eggs and vanilla, scraping sides as necessary, and mix until well incorporated.
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4
Add in salt, baking powder and flour and stir on low until it just starts to come together. Then add the sour cream and continue mixing on low-medium speed until well combined, smooth and there are no lumps of flour.
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5
Tip the batter into your greased pan and spread until level with a spoon/spatula. Sprinkle raspberries all over the cake and press them ever so slightly into the batter. Sprinkle your crumb topping all over the raspberries. You will have enough to cover the cake completely, a good crumb layer is a necessity!
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6
Once you've added the crumb topping, place in the oven for 35-45 minutes (mine took 45 minutes this time round, but previously has taken 35) until risen, golden and a skewer inserted into the centre comes out clean. Remove from oven.
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7
Allow it to completely cool in the pan before transferring to a cutting board and slicing into 12-16 pieces.
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8
Crumb cake will keep in an airtight container, at room temperature for 4 days. The lemon flavour is better on the second day, but the crumb topping won't be as crunchy.
