Preheat your oven to 160 fan (180c or gas mark 4) and line a cupcake/muffin tray with cupcake cases.
In a large bowl cream together your butter and both sugars for about 5 minutes until well mixed and pale. Add your eggs, one at a time, mixing well after each egg.
In a separate bowl combine flour and ovaltine, and in small jug (easier for pouring!) combine your milk, sour cream and vanilla.
Add approx half of the flour mixture into the creamed butter and sugar and mix well. Then add half the wet ingredients, again mixing well. Repeat and then ensure all the ingredients are well combined. I beat by hand when adding the flour and wet ingredients but you could use a hand mixer if you prefer.
Using an ice cream scoop or a tablespoon place a scoop of the mixture into each cupcake case. Then add 2 Maltesers into each case (either regular or white - I used a mixture) and top with another scoop of cake mix.
Bake in the oven for approx 25 minutes. To check if they are cooked insert a skewer into the centre of the cakes - if it comes out clean they're done. Leave to rest in the tray for 5 minutes, then place on a wire rack to cool fully.
Once they are cool you are ready to frost the cupcakes. I used a mixture of both vanilla and chocolate to create a Maltesers effect.
Mix the icing sugar and butter in a bowl for approx 5 minutes until nice and fluffy. I tend to add a little bit of icing sugar at a time to minimise icing sugar dust clouds! Mix the milk and vanilla together and add a little at a time, whilst continuing to mix. Continue mixing until the frosting is light and fluffy (about 3-5mins).
Take approx 6 Maltesers and use a hand held blender/food processer to make Maltester dust and mix this into the vanilla frosting to make your Malteser frosting centre.
Melt the chocolate in a heatproof glass bowl over a saucepan of simmering water. Or alternatively use your microwave. Leave to cool.
Beat together butter, milk, vanilla, and icing sugar till smooth. Again I add the icing sugar a bit at a time to minimise mess. This will take several minutes to achieve a smooth frosting. Add the cooled, melted chocolate and beat again for approx 5 minutes until thick and creamy.
For the Maltesers effect I piped a small circle of vanilla onto each cupcake, and then surrounded it with piped chocolate frosting. Topping each cupcake with a Malteser to finish.