Preheat oven to 350F/ 177C and spray a glass or metal 12x8" rectangle or 9x9" square baking dish with baking spray. Then line it with parchment paper so it comes up the sides.

In a large bowl, combine the sugars, salt and melted butter using a handheld mixer on medium speed until well combined, about 20-30 seconds. Then add the eggs snd vanilla, mixing briefly after each addition. (Don't overwhip the eggs if you want chewier, less cake-like brownies.) This can also be done by hand with a whisk or with a tabletop mixer if needed.

Next using a spatula, not the mixer, sift in the flour and cocoa powder together in about 3 additions, folding each time only until almost totally combined. Once all the flour is in and few streaks remain, fold in 1/2 of the chopped chocolate and the helva chunks. Pour the batter into the prepared baking dish and spread out evenly.

Then spoon the tahini over the batter in little spoonfuls and use a knife or skewer to gently swirl it around to make a marbled effect. Sprinkle the other half of the chocolate on top.

Place in the preheated oven and bake for about 25-30 minutes until the middle still has a slight giggle to it. (If using a 12x8" pan instead of a square, they will bake for a shorter amount of time.) Once they come out of the oven and have cooled slighty, sprinkle a little sea salt over the top.

Let them cool in the pan completely before cutting into squares. Store in an airtight container for 5 days or about a month in the freezer.