Preheat oven to 375 degrees, and line two cookie sheets with parchment or silicone mats.
Mix the sesame seeds and 2 tsp sugar in a shallow bowl, and set aside.
Put the tahini and coconut oil in a large bowl. Microwave for a few seconds to melt the oil. Whisk to combine the two. Add the zest, juice, extract, 2 tablespoons of milk, ½ cup sugar, and salt, and whisk to combine.
Sift the flour and baking soda into the bowl and stir until a dough forms. If the mixture is too crumbly, add another tablespoon of milk and stir to incorporate.
Scoop about 1 tablespoon of dough into your hand. Using your palms roll the dough into a ball, and and then flatten it into a cookie shape. Dip both the tops and bottoms of the cookies in the sesame seed-sugar mixture and place on the prepared pans.
Bake 10 to 12 minutes or until the bottoms are lightly golden. Allow cookies to cool on the pans for a few minutes before transferring to cooling racks.
Once cool, store cookies in an airtight container up to 4 days (either refrigerated or at room temperature). Cookies also freeze well; allow an hour or two to thaw before serving.