Cream the sugar and the butter together until fluffy. I used a hand mixer for this stage.
Add the eggs one by one and mix them in well with a wooden spoon.
Add the vanilla bean paste.
Fold in the flour and baking powder.
Line your slow cooker pot. I use a round 3.5 litre slow cooker, and line it with a large paper cake case (available in pound shops etc). You could also use baking paper.
Spoon half of the cake mixture into the lined pot. Add four to five heaped teaspoons of blueberry jam on top of the cake mixture, then spoon the rest of the cake mixture on top.
Add four to five more heaped teaspoons of jam on top. Use a knife to marble the jam through the cake mixture.
Add the fresh blueberries on top, they will sink in as the cake bakes.
Put the lid on the slow cooker with a tea towel tucked under it to catch drips. Make sure you fold up the sides of the tea towel so they don't hang down over the edges of the slow cooker.
Bake on high for about 1.5-2 hours or until a knife comes out clean from the centre of the cake. The time really varies depending on your slow cooker so keep an eye on it! If the sides start to burn, rotate the bowl within the slow cooker or turn it to low.
When ready, let it cool a little then use the edge of the cake case to pull the cake out of the pot, and leave it to cool fully on a rack.
Make the glaze by mixing a little cold water with the icing sugar to form a paste, then adding the vanilla extract.
When the cake is cold, drizzle the glaze over it.
Serve and enjoy!