Preheat the oven to 180 degrees Celsius, and grease and line a sheet cake tin of your choosing.
Mine is 24 x 24cm.
In a mixing bowl, combine the flours, baking powder (not the soda, we use that later!) and spices, mixing well to combine. Set aside.
Place the butter and sugar into your stand mixer and use the beater the whip the mixture until it is light and fluffy. You can also do this with a hand beater.
Add the maple syrup, continuing to mix until it is incorporated.
Add the eggs, one at a time. Know that the mixture will probably look a little split, and that’s cool. It will return to normal when the flour mixture is added.
Turn the mixer off, and add half the flour. Return it to a low speed, and mix until incorporated. The low speed is so you don’t end up with a dusting of flour across your kitchen. Repeat with the second lot of flour.
Finally, pour the boiling water into a jug with a lip, and add the baking soda. With the beater running, slowly pour the hot water into the cake mixture. Only pour a thin stream at a time, or it will cook the eggs.
Once the water is fully incorporated, pour the batter into the greased baking tin. It will be a thin batter, but don’t panic.
Place the timer on for 10 minutes. During this time, make the streusel. You can use a food processor to roughly chop the nuts, or chop them by hand.
Once they’re chopped, use your hands to massage in the butter and sugar evenly.
When the timer goes off, open the oven and arrange the streusel on top of the cake. The top of the cake should be firm but the interior wet, so push the nuts down a little to break the surface. The reason we’re putting nuts on now is that they will sink if we put them on at the start.
Return the cake to the oven for 15-20 minutes. Once browned, allow to cool in the tin for 10 or so minutes, before gently removing and placing on a cooling rack. Serve with some ice cream or a drizzle of maple syrup.