Heat oven to 180C/160C fan/gas 4.
Lightly butter a deep, round 20cm cake
tin and line the base with a circle of
non-stick baking parchment.
Place the butter in a large bowl and
beat with an electric whisk until light
and fluffy, then add the caster sugar and
lemon zest and beat again. Gradually add
the eggs to the mixture, beating well with
each addition, until fully combined. The
mixture will begin to look glossy – if at
any stage the mixture curdles, beat in a
spoonful of ground almonds and continue
to add the egg until it is all amalgamated.
Stir in the ground almonds, then the
flour, and fold everything carefully
together using a large spoon. Fold
through half the rhubarb, then transfer
the mixture into the prepared cake tin
and scatter with the remaining rhubarb.
Finish with the demerara sugar sprinkled
on top. Bake the cake for 45 mins, or
until a skewer inserted into the middle
comes out clean. Transfer to a wire rack
to cool slightly in the tin, then remove
from the tin. When the cake is cold,
make the topping.
Whip the cream in a large bowl until it
forms soft peaks. In a small bowl, loosen
the lemon curd with about 1 tbsp water
and carefully fold it through the cream,
without overworking. Spread over the
cake, drizzle with a little more lemon
curd and serve immediately.