01 - Line an 8x4 inch loaf pan with parchment paper, allowing overhang on all sides for easy removal of the set halva.
02 - Combine sugar and water in a medium saucepan. Heat over medium heat, stirring constantly until sugar completely dissolves. Bring to a gentle boil and cook without stirring until thermometer reaches 245°F (soft ball stage).
03 - While syrup heats, whisk tahini, matcha powder, and sea salt in a mixing bowl until completely smooth and uniform in color.
04 - Immediately pour hot syrup into the tahini mixture once it reaches temperature. Stir vigorously with a wooden spoon for 20-30 seconds until mixture thickens, appears matte, and begins pulling away from bowl sides.
05 - Quickly scrape mixture into prepared pan. Use spatula to smooth top evenly. Work rapidly as mixture begins setting immediately.
06 - Let halva cool at room temperature for 10 minutes, then refrigerate for at least 1 hour until completely firm and set.
07 - Lift halva from pan using parchment overhang. Cut into 12 even squares. Serve immediately or store refrigerated in airtight container.