Heat oven to 180C/160C fan/gas 4.
Line a 12-hole muffin tin with paper cases.
Sift the flour, cocoa, baking powder and
cinnamon into a bowl. Stir in the sugar
and cranberries. Microwave the chocolate
on Medium for 1-1½ mins, stir, then set aside.
Mix the yogurt and milk with the oil and
egg. Make a well in centre of the dry mix
and gently stir in the liquid. Drizzle half
the chocolate over the mix, gently fold
in until swirled, then repeat with the
remaining chocolate. Take care not to
over-mix. Spoon the mix into the muffin
cases and bake for 15-20 mins until risen
and firm to the touch.