Combine the flours and butter in a food processor; pulse until crumbly. (Alternatively, use a pastry cutter or two knives to cut the butter into the flour.) Stir in the baking powder and salt until incorporated, then stir in the yogurt.
Generously flour a work surface. Turn the dough out there and knead for about 5 minutes, until smooth. Gather it into a disk, wrap in plastic wrap and refrigerate for at least 1 hour or up to overnight. (You’ll be using the floured work space again to roll out the dough.)
Line a baking sheet with parchment paper. Unwrap the dough and let it sit at room temperature for no more than 10 minutes (when pressed with a finger, the dough should hold the indent); re-flour the work space as needed.
Roll out the dough into a rectangle that’s slightly larger than 9 by 18 inches, then trim to straighten the edges as needed.
Use a sharp knife, a cookie cutter or a fluted wheel to cut out the crackers as you like (18 to 36 pieces total). Pierce the dough with the tines of a fork. Transfer to the baking sheet, spacing the pieces of cracker dough 1/2 inch apart. (They will not spread.) The scraps may be re-rolled two times. Refrigerate for 20 minutes.
Meanwhile, preheat the oven to 350 degrees. Whisk together the maple syrup and hot water in a small bowl.
Brush each cracker with the maple syrup mixture, then sprinkle lightly with the togarashi seasoning. Bake (lower rack) for 20 minutes or until golden and crisp, rotating the pan front to back halfway through. Transfer the crackers to a wire rack to cool completely before serving or storing.