Pre-heat the oven to 180°C / 350°F. Line and grease a 23cm x 23cm (9" x 9") baking tin

To make the shortbread base, add cold cubed butter to a mixer with the caster sugar. Beat on a medium speed until well combined

Add in the flour, and mix on a low-medium speed until the flour is well combined. Take the bowl off the mixer stand, and using your hands press the dough into one mass. If the dough is too dry, and a little milk, one teaspoon at a time

Press the dough into the base of the baking pan, and level out

For the frangipane filling, add the butter and sugar to the mixer and beat on a high speed into the butter and sugar are well mixed

Add in the plain flour, vanilla and the eggs, and beat on a high speed until the mixture look pale and creamy

Add in the ground almonds, the ground ginger and the lemon zest. Mix on a med-high speed until the mixture is well combined

Spoon the frangipane mixture over the shortbread base, and level out with a spatula or spoon

Chop the rhubarb into pieces about 2cm long. Sprinkle the pieces over the top of the frangipane and press them until the are almost under the surface

Place the mixture into the oven, and bake for 40-45 minutes. You may need to cover the cake with greaseproof paper or foil for the last 15 minutes to prevent the cake from coming too dark

Once done, leave in the cake tin for about 15 minutes, then using the paper lining, lift onto a cooking rack to fully cool. Dust with a little icing sugar before serving