Preheat oven to 350°F. Grease a 9 x 9 baking pan for thick or 13 x 9 for thin blondies.
Whisk together all purpose flour, baking powder and salt and set aside.
Cream butter with both sugars until light and fluffy, about 3 minutes.
Add the eggs and vanilla and mix until smooth and incorporated.
Add the dry ingredients and stir until just combined.
Add 1/4 cup of the pecans, 1/2 cup pecan pie M&Ms, and 1/3 cup of the white chocolate chips and mix in.
Spread evenly in the pan.
Add the rest of the pecans and pecan pie M&Ms to the top of the blondies by pressing slightly into the dough.
Bake for about 20 - 25 minutes for 9 x 13 pan and 30 - 35 minutes for the 9 x 9 pan.
When blondies are done they will turn a dark caramel color; a toothpick inserted into the middle of the pan should come out almost clean, with some moist crumbs.
Take the blondies out of the oven and sprinkle the remainder of the white chocolate chips onto the blondies.