Preheat the oven to 160 C / Gas 3. Grease a cake tin.
Add the eggs and butter to a bowl and mix well till smooth. Add the glass of sugar and mix well. Once well combined, add the flour and mix well (make sure it is the same glass you used to measure the sugar!). The mixture will be very thick. Finally, stir in any additions you may want to add: chopped chocolate, dried fruit, vanilla extract, etc. Tip the mixture into the prepared tin.
Bake the cake in the preheated oven for 45 to 60 minutes, until it tests done with a skewer.