This is an amalgamation of several recipes and has worked for me countless times. It works with any soft fresh fruit - try blueberries, raspberries, strawberries, cherries - and it's great with tinned peaches, mango or mandarins, too. Makes 24 regular muffins or 30 to 36 small-case muffins.
If using tinned fruit, try to use fruit-juice based options (not syrup); drain well, and reserve the liquid to make up no more than half the total milk amount (250ml).
Use 'extract' not 'essence' - the latter can be very chemically-tasting and has no natural flavourings. Match your extract with your fruit - the pictured examples are raspberry with lemon extract. Almond extract goes well with cherries; vanilla with peaches or almost anything else.