Preheat oven to 325 degrees. Mix the flour and baking soda in a bowl and set aside.
In another bowl cream together the softened butter, brown sugar and granulated sugar. Then add in egg, egg yolk and vanilla until mixed well.
Gradually add flour mixture and mix together until a dough forms.
Then fold in toffee bits.
Using a 1/4 cup measuring cup, scoop out 1/4 cup of dough for each cookie. Roll it in a ball and then split it into 2 separate pieces. Turn each half of the dough so the rough side of the half faces upward. Then stack both halves on top of each other (as in the picture below).
Place the dough rough side up on ungreased baking sheets. Leave about 2 inches between each cookie because they will grow.
Bake for 12-15 minutes or until the edges are golden brown. Do not overbake.