Preheat oven to 350 degrees Fahrenheit and line two cookie sheets with Gefen Parchment Paper or a silicone mat, such as Silpat.

To make the cookies: Stir together flour, baking powder, baking soda and salt in a medium bowl. Using an electric mixer, cream tahini and margarine until very smooth, about two minutes. Add brown sugar, granulated sugar and vanilla sugar and mix until light and fluffy, about three minutes. Beat in egg, vanilla, and orange zest, if desired. Add dry ingredients in two batches, mixing until just blended after each addition. Refrigerate dough for at least 10 minutes, or up to a few hours.

Scoop one tablespoon of dough and roll into a ball. Repeat with remaining dough and set about three inches apart on the lined cookie sheets.

Bake for 10 minutes and remove from oven. (The cookies will still be soft.) With the bottom of a wooden spoon or the backside of a 1/4 teaspoon measuring spoon, gently make an indentation in the center of the cookie that’s deep and wide enough to hold the filling without going all the way through the dough. Return cookies to oven and bake for an additional five minutes, or until lightly browned. Remove from oven and let cool five minutes on baking sheet, then transfer to a wire rack to cool completely.

Combine chocolate, corn syrup, and margarine in a small saucepan over low heat. Stir until melted, smooth and glossy. Alternatively, place the ingredients in a glass bowl and microwave in 30-second intervals, stirring after each one, until the chocolate is almost melted.

Continue stirring to melt the chocolate completely.

Let the chocolate filling cool slightly, and then fill cookie indentations with chocolate.

Sprinkle cookies with sea salt and allow chocolate to set for at least an hour before serving.