Preheat oven to 160 degrees celsius
Grease and line a 27cmx23cm baking pan with some baking paper. Set aside
Using an electric mixer beat the butter and sugar together until light and fluffy, about 3-4 minutes
Add the egg and combine well. Mix in the vanilla essence
Add the flour and baking powder and mix until well combined. Do not add all of the flour at once, you may require more or less. You should have a soft, biscuit like dough
Press about 3/4 of the dough into the baking pan using your hands. Flatten it into a neat rectangle with the back of a measuring cup or using a mini roller. Alternatively you can roll the dough out with a rolling pin on a piece of baking paper, cut the edges neatly and place it into the pan.
Use the back of a chopstick and make little holes in the dough, this will allow the jam to seep through a little. You can also use your finger if you don't have a chopstick
Heat the jam in the microwave for 30 seconds. Give it a good mix so it is free from any lumps. Spread it over the dough. Grate the remaining quarter of the dough on top. Ensure it is spread evenly
Bake on the centre rack for 40-45 minutes until it start to turn slightly brown on top
Remove from the oven and allow it to stand for 10 minutes. To speed up the cooling process you can place a wet kitchen towel underneath the pan
Cut the tart in half, this will prevent it from breaking when lifting it out of the pan. Gently lift the tart, using the overlapping baking paper and place on a flat surface
You can cut them into rectangles or squares once it is slightly cool
Once completely cool dust with icing sugar if you prefer and store in an airtight container for up to a week