Gently melt the butter and chocolate in an ovenproof frying pan, about 23 cm (9 inches) across. Remove from the heat and cool for a couple of minutes.
Beat together the sugars and eggs, then stir in the chocolate mixture followed by the almonds and flour.
Wipe the rim of the frying pan with a damp piece of kitchen paper to neaten, then pour the mixture into the pan. Place in a preheated oven, 180°C (350°F), Gas Mark 4, for 25 minutes until just set. Serve warm with vanilla ice cream.