Preheat oven to 350 degrees. Line a 9x13 inch pan with parchment paper or foil, set aside.
In a small microwave safe bowl melt 3/4 cup of the butter (or in a small saucepan over the stovetop*).
In the bowl of a stand mixer, beat the butter and sugars together until light, about 2 minutes. Add vanilla, then egg and egg yolks one at a time, mixing until just combined.
In a small mixing bowl, whisk together the flour, baking soda and salt. With mixing speed on low, gradually add the dry ingredients mixing until no flour pockets remain. Remove bowl from stand and fold in M&Ms, chocolate chunks and sprinkles.
Spread the dough into the pan creating an even layer. Place in the oven and bake for 25-30 minutes or until the blondies are medium golden brown in color. Remove from oven and allow to cool in pan for 30 minutes before cutting and serving.