# To make the base: Add the butter and caster sugar into the flour until the mixture resembles fine breadcrumbs. Mix in the egg until the mixture starts to look like coarse breadcrumbs. Tip the mixture into the base of the tin, and press it down firmly to give an even layer.
# Chill the base for 10-15 mins until it's firm.
# Set the oven to gas mark 4 or 180°C, and place a solid baking sheet in the oven to heat up.
# To make the filling: Place the butter in a bowl and whisk until soft. Add the caster sugar and cream them together until the mixture is light and fluffy. Add the ground almonds and almond extract. Gradually whisk in the eggs, one at a time, adding a little flour with each egg. Beat in the rest of the flour. Spoon the mixture over the base, and spread level.
# Scatter the blueberries over and press them into the sponge mixture and then top with flaked almonds.
# Place the tin on the hot baking sheet in the centre of the oven, and bake for 40-45 mins or until the mixture is a light-golden colour. Remove from the oven and leave to cool in the tin for 10-15 mins, and transfer to a wire rack to cool.
# When the traybake is cold, dus