Preheat oven to 180C and grease and line a 23-centimetre, round cake tin with baking paper. Don't use a spring-form tin as the toffee syrup will leak out.

Combine the wattleseed and boiling water in a small bowl and cool to room temperature.

Place the caster sugar and water in a small saucepan over medium heat and stir with a wooden spoon until the sugar has melted. Bring to the boil and cook for 10 minutes until light golden brown. Swirl the pan to distribute the colour evenly, then pour into the cake tin.

Quickly place the pineapple pieces on the toffee to cover the base. Set aside.

In an electric mixer, beat the egg, macadamia oil and brown sugar until sugar has dissolved.

Remove the bowl and stir in wattleseed and crushed pineapple.

Sift flours and bicarbonate of soda and fold through the mix. Pour into the cake tin, spreading over the toffee and pineapple.

Bake on the middle shelf for one hour or until a skewer comes out clean. Remove from the oven and leave to cool in the tin until warm. Invert the tin onto a flat plate and gently lift it off the cake.

Peel off the baking paper to what is now the top of the cake (the cake will be quite fragile so the edges may break away a little).