Preheat the oven to 180C/350F/Gas 4. Generously butter 4 x heatproof cups or ramekins that are approximately 7.5 cm/3 in in diameter and 4 cm/1 1/2 in deep, using 25 g/1 oz of the butter.
Melt the chocolate in a heatproof bowl set over a pan of simmering water.
Remove from the heat and whisk in the remaining 75g of the butter until melted. Stir in the whiskey and set aside to cool.
Place the egg whites in a bowl and whisk until stiff peaks have formed.
Whisk in half of the sugar, a third at a time, whisking well after each addition until stiff and very shiny.
In a separate bowl, beat the remaining sugar and egg yolks until pale and fluffy, then beat into the cooled chocolate mixture.
Fold in the meringue and use to fill the prepared cups two-thirds full.
Arrange on a baking sheet and bake for 12 minutes until well risen but still with a slight wobble in the middle.
To serve, arrange the Irish whiskey chocolate fondants and serving plates with small jugs of pouring cream