Preheat the oven to 180C/350F/Gas 4. Grease a 10-inch bundt pan, and set aside.
Whisk together the flour, baking powder, baking soda, salt, and lemon zest. Set aside.
Whisk together the eggs. Add the sugar, and whisk until combined. Add the lemon extract, melted butter, and yogurt, and whisk until combined. Fold in the dry ingredients.
Pour half of the batter into the prepared pan.
For the Cheesecake Swirl
Whisk together the cream cheese and sugar until combined. Beat in the egg and lemon extract, then fold in the flour.
Spread the cheesecake mixture evenly over the cake batter (making sure not to let it touch the sides and middle), then pour the remaining cake batter on top.
Bake for 50 - 60 minutes or until a toothpick inserted into the centre comes out clean. Let cool in the pan for 10 minutes before inverting the cake onto a serving plate or cake stand. Allow to cool completely before glazing.
For the Glaze
Whisk together the icing sugar, lemon extract, and heavy cream. Add more icing sugar if too runny, or more cream if too thick. The glaze should be fairly thick, but pourable. Drizzle over the cooled cake, and serve.
Notes
*Make your own cake flour! Weigh out 3 cups (375g) of plain/all-purpose flour, remove 6 tablespoons, and replace with 6 tablespoons of cornflour/cornstarch. Sift well.Leftovers can be stored in the fridge for up to 2 - 3 days. You can bake this cake 1 day in advance. Allow to cool completely, then cover tightly and keep in the fridge until ready to glaze and serve.This cake also freezes well for up to 2 months. Thaw overnight in the fridge before serving.