For the cake: 170g unsalted butter, softened and 170g caster (or granulated) sugar, plus...
170g plain flour with ½ tsp salt mixed in
1 tsp bicarbonate of soda plus 1/2 tsp baking powder
50g poppy seeds
Grated rind or zest of 2 large or 3 medium lemons
4 eggs, separated (yolks into a 1 litre jug, whites into a big, clean bowl)
170g wholemilk or Greek yoghurt
2 tsp vanilla extract
For the syrup:
Juice of the 2 large or 3 medium lemons
5 tbsp icing sugar
Zest of 1 lemon, pared off with vegetable peeler and cut into thin, short strips (remove white pith as much as possible)
For decoration:1 tbsp icing sugar
Heat the oven to 180C/350F/gas mark 4. Butter a 23cm springform cake tin. Dust this with flour to stop the cake sticking.
Sieve into a medium-sized bowl the flour, salt, bicarbonate of soda and baking powder. Stir in the poppy seeds and grated lemon. In a bigger bowl, beat together the butter and 120g of the sugar until light and fluffy. In the jug, whisk together the egg yolks, yoghurt and vanilla extract. Beat the egg whites vigorously with a pinch of salt until they hold soft peaks. Add the remaining 50g of sugar slowly, beating until the meringue mix holds stiff peaks.
Take the bowl with the butter and sugar, and beat in the flour mixture and the egg mixture alternately starting and ending with the flour. Then stir about a third of the meringue mixture into this batter to lighten it, then gently fold in the rest (with a metal spoon). Spoon the cake mix into the tin, smooth the top and bake for 40-45 minutes, until a toothpick or sharp knife comes out clean.
While the cake is baking, make the syrup. Combine the lemon juice, icing sugar and zest in a small saucepan and heat gently, stirring, until the sugar is dissolved. Simmer for two minutes, then remove from the heat.
Take the cake out of the oven and spike all over the top with a skewer, trying not to penetrate the base of the cake. Pour or spoon the syrup over slowly, letting it trickle over the top and down the sides. Leave to cool in the tin, then carefully turn out onto an attractive plate before dusting with icing sugar. This cake will keep well for several days if wrapped in cling-film and placed in a cool larder or fridge. Best eaten with good quality tea and a healthy appetite, and don't forget to check your teeth afterwards in case those mischievous seeds have become lodged in the gaps!!