Pre-heat the oven to 375°F.
Grease a 9-inch or 8-inch loaf pan with butter and line it with a parchment paper sling; butter the paper; set the pan aside.
In the bowl of a stand mixer, fitted with the paddle attachment, place butter, sugar, lemon zest and vanilla extract; beat on high speed for 3 to 4 minutes, until light; lower speed to medium.
Add eggs, in three additions, scraping down the sides of the bowl a few times as necessary.
The mix may split a little but don’t worry; It’ll come back together once you add the dry ingredients.
In a separate bowl, whisk together flour, baking powder, salt and almond flour.
With the stand mixer on low, add the dry ingredients in three additions, mixing just until no white specks remain.
Fold in, by hand. about 3/4 of the blueberries; scoop batter into the prepared loaf pan.
Place in the oven and bake for 15 minutes.
Remove from the oven; sprinkle the remaining blueberries over the top of the cake.
Return to the oven for another 15 to 20 minutes or until cake is golden brown but still uncooked.
Open oven door, cover loosely with foil and continue to cook for another 25 to 30 minutes (less for a 9-inch pan, more for an 8-inch pan) or until risen and cooked and a knife inserted into the middle of the cake comes out clean.
Remove from oven and set aside, in its pan, to cool for 10 minutes before removing cake from pan and placing on a wire rack to cool completely.
When cake is cool, make the icing:
Add lemon juice and icing sugar to a bowl; whisk together until smooth, adding a bit more juice if necessary, just until the icing moves when you tilt the bowl.
Pour over the cake and gently spread out.
The blueberries on the top of the cake may bleed into the icing a little, but this will add to the look.
Let icing set, for about 30 minutes; slice and serve.
