1. To make the dough, cream butter and sugar until pale and fluffy on low speed. Add egg and vanilla, then mix on low speed until just combined. Add salt and flours, then gently mix until it just comes together. Do not overmix dough.
2. Pat dough into a disc, and wrap in cling film. Refrigerate 30 minutes.
3. To make the cookies, remove dough and allow to sit on the counter 5-7 minutes, until it’s workable but still cold. Roll out dough to 1/4 inch thickness. Cut out 12-14 hearts using your 2-2 1/2 inch heart shaped cookie cutter. Place cookies on a baking sheet and bake 8-10 minutes at 350°F. While the first batch of cookies is baking, roll out dough again and cut out 12-14 more hearts using 2-2 1/2 in cookie cutter. With the small heart cookie cutter, cut a heart out of each cookie. Bake this batch, including the mini hearts, 8-10 minutes. Repeat this process until all dough is used up.
4. Allow cookies to cool completely before assembly. Place 1 tsp. of jam on each full cookie. Dust a light layer of confectioner’s sugar on each cookie with a cut out heart along with the mini hearts. Place the cut out heart on top of the full cookie as if it were a lid. Use the small hearts to decorate the platter of cookies.