If you find a few gaps in the slice once you have placed the topping, that is fine, it will spread as it cooks. Other berries are just as delicious. This is wonderfully moist, great with a morning coffee or as a wee treat for dessert.
Preheat the oven to 180C and lightly grease a 20 x 30cm tin.
Place the flour, sugar and butter into a bowl, working it together until it resembles fine breadcrumbs. Add the water and mix until combined. Press into the base of the tin and bake for 15 minutes. Allow to cool.
Sprinkle over the blueberries. For the topping, cream the butter and sugar. Add the egg and beat through, then the ground almonds, baking powder and almond essence. Spread carefully over the blueberries then sprinkle with sliced almonds. Place into an oven for 30 minutes or until set in the middle. Remove and cool before cutting.