In a bowl beat together butter and sugar until light and fluffy.
In a large bowl mix flour, cornflour, xanthan gum together until fully combined.
Add butter and sugar mixture to the large bowl with the flour mixture.
Add water and with your hands knead together and will resemble large crumbs but continue to knead as it will eventually form a shortbread dough.
Place your dough onto a floured surface. Using a rolling pin roll out your dough evenly until around ¼ inch thick.
Using your preferred size cookie cutter (I used a 2 ½ inch cookie cutter) cut out the cookies and carefully place them on a lined baking tray.
Once on the baking tray use the small heart cookie cutter and cut out the center of half the cookies. (I like to also bake the small heart if there is additional space on the baking sheet).
Place the baking tray in the refrigerator for 30 minutes as this allows the dough to firm up and help reduce the cookies spreading while baking.
Preheat the oven to 170°C/325°F/Gas mark 3
Bake in the oven for 15-20 minutes until they start to turn slightly golden on the edges but still pale on top.
Once baked leave them on the baking tray to slightly cool before moving to a cooling rack as they may still be soft to touch when removed from the oven but will firm up as they cool.
Once fully cooled spread ½ teaspoon of jam on the full round cookie and top with the cut out heart cookie. You can dust with powdered sugar if desired or keep plain for a more traditional jammy dodger biscuit.