Heat the oven to 350 degrees F with a rack in the center of the oven. Grease
the baking pan with 1 tablespoon unsalted butter or solid vegetable shortening.
In a large mixing bowl, beat the butter with the mixer on high speed until
Gradually add the dark brown sugar and continue to beat until light
and fluffy, about 2 minutes. Some small nuggets of dark brown sugar may remain
in the mixture, but that is okay. Move the beaters around the bowl and scrape
down the sides of the bowl with a rubber spatula several times while mixing.
Lower the mixer speed to medium and beat in the corn syrup and vanilla extract,
then stir in the oats with a wooden spoon.
Spread the batter in the prepared
pan and bake for 16 minutes.
Remove from the oven and cool in the pan on a wire
rack until lukewarm.
While the bars are baking and cooling, make the glaze.
Place the chocolate
chips and peanut butter in a small saucepan and stir over low heat until the
chocolate melts and the mixture is smooth.
Spread the mixture over the lukewarm
bars, then cool completely or refrigerate until cold. Cut into bars when cold.
The bars can be stored in a covered tin at room temperature for up to 1
week. Cushion the bars between layers of plastic wrap or wax paper to protect
To freeze, allow them to cool completely after baking, then spread
them on a baking sheet and place in the freezer for at least 3 hours.
When the bars are thoroughly frozen, stack them in freezer-strength zip-type
gallon-size plastic bags for up to 3 months. Use a waterproof marker to note
the contents of the bags and the date.
Defrost them in the bags at room temperature
for 1 to 2 hours.