Heat oven to 160C/140C fan/gas 3.
Grease and line a 20cm square tin with
baking parchment. Put the butter, sugar,
eggs, yogurt, flour and baking powder in
a large bowl and beat with an electric
whisk until smooth. Tip into your cake tin
and smooth the top. Bake for 45-50 mins
until risen and golden, and a skewer
inserted comes out clean. Leave to cool
for 10 mins in the tin, then turn out onto
a wire rack to cool completely.
Grind the lavender to a powder using
a pestle and mortar. To make the butter
icing, beat the butter and icing sugar
together until pale and fluffy. Divide the
mixture into 2 bowls, add the lemon
zest to one batch and the lavender to
the other, then mix each to combine.
Transfer the icings to 2 piping bags.
When the sponge has completely
cooled, use a large serrated knife to
remove the top and give you a flat
surface. Flip the cake over so the
flattest side becomes the top. Carefully trim off the edges, then cut the sponge
into 16 squares. Use a ruler if you want
them to be the same size. Brush the top
and sides of each sponge square with a
little jam. Pipe a small dome of butter
icing onto each sponge, 8 with lavender
icing and 8 with lemon. Chill the cakes
for at least 1 hr.
Sieve the fondant icing sugar into a large
bowl, and add enough water to make a
thick but pourable icing. Spoon a little
white icing into a sandwich bag or piping
bag to use later. Divide the remaining
icing into 2 bowls, dye one batch lemon
yellow and the other pale lilac.
Remove the sponges from the fridge
and transfer to a wire rack, sitting the
rack on a tray to catch any drips. Spoon
a little icing over each sponge, lilac for
the lavender-flavoured fancies and
yellow for the lemon. Use a small palette
knife to spread the icing down the sides
of the sponge to completely cover each
one. Leave to set for 30 mins, then cover
the cakes with a second layer of icing
to give a smooth surface. Drizzle the
white icing over the cakes and decorate
with a little lemon zest and lavender
buds. Leave to set for 1 hr at room
temperature before serving. Will last
2-3 days in a tin.