Preheat the oven to 175°C (350°F) Prepare an 8x8 inch pan lined with aluminum foil then buttered generously on all sides.
In a medium-sized bowl whisk together the flour, salt, and baking powder. Set aside.
Place the butter, tahini, and chopped white chocolate in a heat-proof bowl, then place it on top of a medium pot filled with about 2.5cm of simmering water. The water should not be touching the bottom of the bowl. Stir occasionally until the butter and white chocolate have melted. Set aside and allow to cool slightly. Alternatively, you can use a microwave, place the ingredients into a bowl, and microwave in 15-second bursts, stirring occasionally until everything has melted. After the chocolate mixture has slightly cooled, whisk in the brown sugar.
Add the egg + egg yolks + vanilla and whisk well, the mixture will look thick and glossy.
Using a spatula fold in your dry ingredients (flour + baking powder + salt) until everything is well combined with no lumps visible.
Very gently fold in the crumbled halva into the mixture (try not to break the halva into smaller pieces as you fold.)
Pour the mixture into the prepared baking pan and sprinkle generously with sesame seeds and flaky salt. Place in the oven and bake for 20-25 minutes or until the surface is golden brown and puffy, there should be a slight jiggle in the center. Do not overbake or they will dry out, they will continue to set up as they cool.
Take the pan out of the oven and allow the blondies to completely cool.
Using the ends of the aluminum foil, lift the blondies and cut into 16 squares (squares of heaven) and enjoy with a lovely cup of coffee.
Keeps up to 5 days in an airtight container.