Heat oven to 180C/fan 160C/gas 4.
Grease a 20cm springform cake tin or line a
similar-size cake tin with baking paper. Using
an electric mixer, combine 200g butter and
200g sugar in a large bowl. Beat until light
and creamy, about 2 mins, then add the
eggs, one at a time, beating well after you
add each one. Tip in the flour and baking
powder, mix for a few secs, then add the
orange juice, zest of 2 oranges and poppy
seeds. Stir everything together, then pour into
the cake tin. Bake for 50 mins, then remove
from the oven. Cool completely in the tin.
Meanwhile, make the candied orange
zest by combining the remaining zest (finely sliced), 25g
sugar and 100ml water in a small pan. Bring
to the boil and cook for 5 mins until thick.
Remove the zest with a slotted spoon onto
a sheet of non-stick baking paper.
For the sauce, heat the cream in a small
pan until nearly boiling. Put the chocolate
and remaining butter into a bowl, then pour
the hot cream over it and leave for 1 min to
melt. Stir together until smooth, then let it sit
until the cake is cool (if it hardens, just reheat
gently). Drizzle the sauce over the cake,
sprinkle with the candied zest and serve.