Pre-heat oven to 180 C/350 F, Line a 9 inch square tin with greaseproof paper so that the base and sides are covered – use a few dabs of butter to get the paper to stick to the pan.
While the oven is heating up, place the 20 g of walnuts on a tray and toast for 5 – 8 minutes. Cool, then place in a food processor and pulse until finely chopped. Don’t take it too far otherwise you will have a nut paste rather than a nut flour. Set aside.
Place the Speculoo biscuits in a food processor and blitz to fine crumbs. Add the flour, oats, ground almonds, the ground walnuts and ginger and pulse a couple of times to combine. Add the cold butter and pulse until the mixture looks like coarse, damp sand.
Set aside 1 cup of this mixture for the topping and tip the rest into the prepared tin. Pat it level – don’t press down too hard or it will be tough – then bake for 15 minutes.
While the base is baking, get the filling ready; sort through the fruit and discard any mouldy ones.
Using an electric mixer and a medium sized bowl, whisk the egg and sugar until coffee coloured and creamy – about 2 minutes. Then add the almond meal and salt and whisk again. Fold in the berries.
After the base has been in the oven for 15 minutes, remove it and top with the filling – covering the hot base as evenly as you can with the fruit. Sprinkle over the chopped walnuts and the reserved topping. Bake for 30-35 minutes until golden brown.
Cool in the tin for 10 minutes, then using the lining paper as handles, lift out and place on a wire rack to cool completely before glazing.
Combine glaze ingredients together until smooth and drizzle over the top. Slice into 16 squares (4 x 4)
Stores brilliantly, covered in the fridge for 4-5 days.