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, and salt. Set aside.
Whisk together the eggs. Add the sugar, and whisk until combined. Add the vanilla, melted butter, yogurt, and peanut butter, and whisk until combined. Fold in the dry ingredients.
Pour half of the batter into the prepared pan. Spoon the jam over the batter without touching the sides of the pan, and top with the remaining batter.
Bake for 45 - 50 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, vanilla, and milk until smooth. Add more milk if too thick, or more icing sugar if too runny.
Drizzle over the cooled cake.
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, covered, 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.