Make the roux - In a small saucepan, whisk together the water, milk & flour - whisk until no lumps remain. Heat this mixture over a medium low heat, stirring constantly. The mixture will thicken (about 3-5 minutes). Remove from the heat and set aside.
Make the dough - Whisk together the flour, sugar, matcha, instant yeast, and salt in the bowl of a stand mixer.
To the roux add the butter, milk, vanilla, and egg & then add to the dry ingredients and with the dough hook, knead for a few minutes until just combined.
Knead the dough for about 10 minutes - it will feel elastic & slightly sticky. Knead the dough into a ball shape & place into a greased bowl. Cover and place in a warm spot to rise for 1 1/2 hours
Make the turtles - After the dough has proved, divide it into 8 equally sized pieces. Reserve 2 of the pieces for the heads & feet of the turtles. Flatten the 6 pieces of dough into about a 4-5" circle & add 15g of chopped white chocolate to the centre, pressing the chocolate into the dough. Fold the dough up & around the white chocolate, pressing the dough together to ensure it is well sealed. Flip over the dough so the sealed side is facing down - repeat with the other 5 pieces of dough & the turtle bodies are done.
Place the turtle bodies on a parchment lined baking sheet, leaving 2" in between each turtle. Take 1 of the reserved balls of dough & divide it into 6 equally sized pieces. Roll each piece into a sphere & gently pinch one end of the sphere, slip the pinched end under the turtle body & press the body down at their meeting point, repeat until all of the bodies have heads. Take the other reserved ball of dough & divide it into 6 equally sized pieces & then divide each of these pieces into 4 small pieces leaving you with 4 small balls of dough per turtle for the feet. Shape each of the 4 small balls of dough into an oval, pinching one end of each oval. Slip the pinched ends under the turtle body placing them where the turtle's feet need to be. Once all turtles have heads & feet, make the eyes by taking 2 black sesame seeds & place them onto each head, gently pressing them into the dough with a toothpick. Cover the completed turtle rolls with cling film & put in a warm place to prove for about 30 minutes.
Make the crunch - In a small bowl whisk together the crunch ingredients until smooth. Cover with cling film and leave to rise while the turtles are proving. When the turtles have risen, pre-heat the oven to 170c. Stir the crunch topping until smooth & then coat the top of each turtle body, spreading it evenly with a spoon until all of the topping is used up. Sprinkle with sugar & then bake the rolls for 20 minutes
Remove from the oven and place the turtles on a rack to cool for about 10-15 minutes. Enjoy turtles while still warm from the oven, otherwise store in an airtight container.