Heat oven to 180C/160C fan/gas 4.
Line a 20 x 30cm baking or roasting tin
with baking parchment. Beat together
the butter, flour, sugar, baking powder,
eggs, yogurt and vanilla. Stir in the
chopped cherries and snipped
marshmallows. Scrape into the tin and
bake for 25-35 mins until a skewer
poked in comes out clean. Cool.
To decorate, put the marshmallows
into a pan with the milk and gently
melt, stirring. Scrape into a bowl and
cool, stirring occasionally, until thick
enough to spread. Spread over the
cake, dot over the halved cherries
and slice into 15 squares.