4 chocolate toffee bars such as Heath or Skor, chopped
Preheat the oven to 375 F (190 C) and lightly spray 12 muffin cups with nonstick spray.
In a large mixing bowl, combine flour, baking powder, baking soda, and salt. Gently whisk to combine and aerate dry ingredients for about 30 seconds.
In a separate, smaller bowl, combine sugar, vegetable oil, egg and egg yolk, and plain yogurt. Whisk until everything is smooth.
Pour wet ingredients into dry ingredients and quickly combine with a rubber spatula. Gently fold the two mixtures together just until moistened. Try not to stir for more than 15 seconds. Add toffee bits and gently fold together.
Divide the batter evenly between 12 muffin cups.
Bake for 18 to 20 minutes.
Allow to cool just long enough so that you can touch them without burning yourself. Remove gently to wire racks to cool. Removing them quickly will avoid soggy bottomed muffins.
These muffins are best eaten warm so either eat them right away, or give them about 15 seconds in the microwave