Grease an 8-inch square pan with butter or coconut oil, then line with parchment paper, leaving an overhang on two sides.
In a large bowl, cream butter, vanilla, and coconut sugar with an electric mixer until fluffy. Add tahini and mix until combined. Add almond flour, brown rice flour, and salt. Mix on low speed until completely incorporated.
Press the dough evenly into prepared pan. Freeze for 30 minutes. Preheat oven to 350 degrees Fahrenheit.
Once dough has chilled, with a knife, score shortbread into 18 pieces. Bake for 30 to 35 minutes, or until golden. At the 30 minute mark, lightly cover with foil to keep from over-browning.
Allow shortbread to cool completely in pan on wire rack. Using parchment flaps, remove from pan to cutting board. Cut into scored pieces. Dip cookies into melted chocolate, place on a piece of parchment. Sprinkle with sesame seeds if desired. Allow chocolate to harden before storing in airtight container.