In a large bowl, combine the gluten-free flour, sugar, and salt.

Add the cubed cold butter and mix until you achieve a crumbly texture.

Incorporate the egg, milk, and vanilla extract into the mixture. Stir until a dough forms. If too sticky, sprinkle in a little extra flour.

Wrap the dough in plastic wrap and refrigerate it for about 30 minutes.

On a floured surface, roll out the dough to about 1/4 inch thick.

Cut the dough into rectangles (about 3 by 4 inches).

Place a spoonful of your chosen jam in the center of half the rectangles. Be careful not to overfill.

Place the remaining rectangles on top and press the edges to seal. Use a fork to crimp the edges.

Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.

Place your tarts on the sheet and bake for 20 minutes or until golden brown.

Let them cool slightly, then make your icing by mixing powdered sugar with milk until smooth. Drizzle over cooled tarts.