Coffee Streusel Slice

This slice is a golden oldie, you know the type of slice grandma used to make.  Buttery, deliciousness that brings back wonderful memories of times with family enjoying amazing sweet treats that grandma made with love.
125g butter
1/4 cup brown sugar
1 cup plain flour
1/4 cup self-raising flour
400g can sweetened condensed milk
30g butter
2 tablespoons maple syrup
3 teaspoons coffee substitute (granulated or powdered)
1/2 cup walnut chopped roughly
1 cup plain flour
2 teaspoons cinnamon
1/3 cup brown sugar, firmly packed
125g butter
Cream butter and sugar until combined and stir in sifted flours
Mix to form a firm dough
Press evenly over base of well-greased (or line with baking paper) 30cm x 25cm baking tin
Bake in moderate oven for 10 until starting to brown around the edges
Combine condensed milk, butter, golden syrup and coffee in saucepan stir over medium heat until mixtures begins to bubble on base of pan. Continue stirring briskly for about 3 minutes, or until mixture is thick and beginning to catch on base of pan.
Pour over the cooled base
Sprinkle walnuts over the top
Sift dry ingredients into mixing bowl, rub in butter
Mix until a firm dough
Refrigerate 30 minutes before grating coarsely over the filling
Bake in moderate oven for 10 to 15 minutes, or until the topping is firm to the touch.
Stand 15 minutes and leave to cool in tin before cutting into slices or squares