Beat the butter and sugar for the muffins until pale and fluffy.
Crack the eggs in a bowl and whisk. Add gradually to the mixture, mixing each time. If the mixture begins to split, add a little of the flour.
Fold in the flour, nutmeg and cinnamon, mix well.
Spoon about two heaped teaspoons of the filling into each cupcake case in a muffin tin.
Bake for 25 minutes until cooked through.
Once cooked, remove from the tin and place the cupcakes on wire rack to cool.
Whilst they are cooling, make the pear purée by peeling, coring and chopping the pears into small pieces.
Put the pieces into a saucepan with the brown sugar and water, cover with a lid and cook for 15 minutes stirring occasionally and bashing with the wooden spoon to make them mushy. Take the lid off and cook for another 5 minutes to reduce down.
Once the pears are soft and mushy (a little like a jam), remove from the heat and leave to cool. To make the frosting, whisk the butter, add the icing sugar and vanilla extract and whisk well together.
To fill the muffins, scoop out a hole in the top of each cooled cupcake.
Fill each hole with a teaspoon of pear purée.
Pipe the butter icing onto each cupcake to cover the hole and purée.