Beat the eggs in a large bowl with 100 g (3 1/2 oz) of the icing sugar, the cream, ground almonds and vanilla extract, if using. Preheat the oven to 200°C (400°F), Gas Mark 6.
Melt the butter in a large ovenproof frying pan and pour in the egg mixture. Cook very gently for 8–10 minutes, stirring occasionally, until the egg just begins to set. Scatter over the flaked almonds and sprinkle with the remaining icing sugar, then place in the preheated oven for about 10 minutes, until set.
Remove the pan from the oven and cook under a preheated grill for 2–3 minutes, until golden, then cool slightly and cut into slices. Serve with vanilla ice cream or crème fraîche.