Preheat the oven to 180ºC/350ºF/gas 4. Rub a 20cm cake tin with butter.
Whiz the butter and sugar in a food processor until light and fluffy. Add the egg yolks, one at a time, while the motor is running, then the lemon zest and juice.
When the mixture is nice and smooth, pulse in the flour and almonds and finally the milk. Don't mix it too much – just enough to combine. Spoon the mixture into a bowl, stir in the poppy seeds and put to one side.
In a very clean bowl, whisk the egg whites until they form soft peaks. Beat in the remaining 1 tablespoon of sugar until smooth. Stir a spoonful of egg white into the almond mixture. Add the rest of the egg white and fold together carefully – you don't want to beat the bubbles out of the egg white.
Spoon into the prepared cake tin and smooth the mix out evenly with the back of a spoon. Place on the middle shelf of your preheated oven and bake for about 45 minutes until cooked through, risen and golden brown.
When cool, sift the icing sugar and mixed spice over the top of the cake and serve with dollops of crème fraîche.
The butter needs to be very soft, so take it out of the fridge in advance.