In a large bowl, gently whisk together the flour, sugar and baking powder and salt, make a well in the middle and add the slightly beaten egg and yolk, vanilla and cubed butter. With a fork mix together until dough slightly comes together, then turn mixture onto a lightly floured flat surface and work gently to form a soft dough. Wrap in plastic and refrigerate for 30 minutes.
FOR THE FILLING
In a medium sauce pan add the strawberries, sugar and cornstarch, cook over medium heat until thickened approximately 10 minutes, remove to a medium-sized bowl and let cool completely. It will thicken even more as it cools.
Meanwhile, Pre-heat oven to 340F (170C), line 1-2 baking sheets with parchment paper.
Remove the dough from the fridge, knead the dough a couple of times to soften it up. Place the dough on a floured flat surface.
Roll out 1/2 the dough (easier to work with) at a time to ⅛ inch thickness (or a little thicker if you prefer) and cut out with medium to large cookie cutters. Flower, shape or heart or even round.
In the middle of each cookie add approximately 1-2 teaspoons of strawberry filling depending on the size, top with a second cookie and seal the edges with fingers dipped in water.
Continue until all the cut outs are complete.
Bake for approximately 12-15 minutes, until lightly golden, (if you make tarts they will need approximately 5 minutes longer). Let cool 5-10 minutes on the baking sheet then move to a wire rack to cool completely, dust with powdered sugar before serving. Enjoy!
** Depending on size of cutter the recipe makes approximately 10 sandwich cookies and 1-3 tarts.
Notes
The dough can also be made in a food processor.You could make 10 medium sandwich cookies (more or less depending on the size of your cutters) and one 4 inch tart.If they last that long you can store your baked cookies in an airtight container at room temperature for 3-4 days! I like to layer them with parchment paper to prevent sticking.You can freeze the completely cooled jam sandwich cookies. Wrap in plastic wrap and freeze in a freezer safe container for up to 3 months. You could also freeze unbaked, freeze until firm on a baking sheet, then move to a freezer container. Bake from frozen.