Whisk flours, baking powder and salt together in a medium bowl. With a knife cut little pieces of the butter into the flour. Then with two knives cut the butter into the flour until mealy, smaller little bits of butter than in a pie dough.
Stir in ⅔ cup warm water with a fork until a shaggy dough forms.
Turn out onto a floured surface and knead 3-4 minutes until smooth, soft, and not sticky.
Cut the dough into 2-oz pieces for taco-sized tortillas or 3-oz pieces for burrito-sized tortillas. You will have 8 to 9 small pieces or 4 to 5 larger pieces. Shape pieces into a ball.
Cover with a very light kitchen towel or plastic wrap. Be careful that your room isn’t too hot. Let the dough rest 30 minutes and up to two hours.
Roll out each ball to about 9 to 10 inches (taco) or 11 to 12 inches (burrito) in diameter, or till you can see the counter start to come through.
(A tortilla press is nice to flatten the ball into a disk to get things going, but ultimately a rolling pin works best. The tortilla press is unnecessary if you don’t have one)
Heat a 12 inch non-stick or cast-iron pan (do not add any oil) on medium-high.
Lay the tortilla in the pan and cook until it puffs and little brown spots on the underside appear. Turn with tongs and cook.
Each tortilla takes about 45-60 seconds. You don’t really want the tortilla to brown at all.