Next, I prepare the streusel topping. I rub the lemon zest into the sugar until fragrant, which helps release all those wonderful citrus oils. Then I mix in the softened butter and vanilla before adding the gluten-free flour blend, almond flour, xanthan gum, and salt. The mixture quickly transforms into buttery crumbs that will bake into a crisp golden topping.
For the cake batter, I once again rub the lemon zest into the sugar before whisking in the buttermilk, melted butter, oil, eggs, and vanilla. The batter becomes silky smooth and fragrant. Then I add the dry ingredients and whisk just until everything is combined. I’ve learned that overmixing can affect the texture, so I stop as soon as the batter is smooth.
Finally, I spread the batter evenly into my prepared baking pan. I spoon the cooled blueberry filling over the top and gently spread it into an even layer. Then I generously crumble the streusel topping over everything. After baking for about 40 minutes, the crumb topping turns beautifully golden while the blueberries bubble underneath. I let the cake cool until warm before slicing and serving.
Pro Tips for Best Results
I tested this recipe with both fresh and frozen blueberries, and both work wonderfully. If using frozen berries, there’s no need to thaw them before making the filling.
Another thing I learned is that cooling the blueberry filling before assembling the cake helps keep the layers distinct and prevents the batter from becoming too loose.
Don’t skip rubbing the lemon zest into the sugar. It creates a much stronger lemon flavor and makes the entire cake taste brighter and fresher.
Common Mistakes to Avoid
The biggest mistake I made the first time was adding warm blueberry filling directly onto the cake batter. It caused the layers to blend together more than I wanted. (See the next page below to continue…)