In a medium bowl combine the flour, baking soda, and salt. Set aside.
In a large bowl cream together the butter, brown sugar, and sugar.
Add in the egg and vanilla and mix well.
Add the flour mixture to the butter mixture and mix until well combined.
Fold in the chocolate chips and all but 9 of the Cadbury egg thirds.
Spread the batter into an 8 x 8 baking dish. Press the remaining 9 Cadbury egg pieces into the top of the batter in the pan. Sprinkle with the sprinkles if desired.
Bake for 23-25 minutes or until the top of the blondies is golden brown.