Pre-heat the oven to 160C/325F/Gas 3. Line a 900g/2lb loaf tin with baking parchment.
Cream the butter with the sugar in a food mixer until pale and fluffy. In a separate bowl sift together the flour and baking powder then mix with the almonds.
Lightly beat the eggs then fold them into the butter mixture in two or three sessions, beating them in thoroughly each time. If the mixture looks as if it is about to curdle, stir in some of the flour.
Grate the zest from the lemon and mix it with the thyme leaves. Pound the two together with a pestle, or some other heavy weight, and stir into the cake mixture.
Gradually mix in the flour, baking powder and almonds.
Spoon the cake mixture into the lined tin and bake for 45 minutes (if dividing the mixture into smaller tins reduce the time accordingly).
For the topping, dissolve the sugar in the juice of the lemons over a moderate heat and stir in the thyme leaves (a few flowers would be good here too). As the cake comes from the oven, spike the surface with a skewer and spoon over the syrup.
Leave to cool and serve in slices with thick yoghurt.