1/2 cup salted butter, melted
2 1/2 cups old-fashioned rolled oats
1 cup brown sugar
1/2 cup semisweet chips or 6 ounces dark chocolate
1 1/2 tablespoons heavy cream
1 teaspoon vanilla
Preheat oven to 350 degrees F and line 2 baking sheets with parchment paper or a silicone liner or foil that is then greased well. Don’t use waxed paper!
Blend the melted butter, sugar, egg and vanilla, mixing until smooth, then stir in the oats. Drop by scant teaspoons onto the prepared baking sheets, 3 inches apart. Bake for 8 to 10 minutes, just until the cookies have spread and the edges have browned.
Cool for a few moments on the baking sheets before carefully transferring to cooling racks. The cookies will firm up as they cool. Repeat with remaining dough.
To make the filling, put the chocolate chips and cream into a bowl and microwave on high for 1 minute. Stir well. Microwave in 10-second bursts as needed, stirring well after each, until the chocolate is melted and the mixture is smooth.
Slick a generous amount of this mixture on the flat side of a cookie and top it with another, pressing to spread the filling out to the edges—some of it may come through the “lace” of the cookie, but this is no bad thing to chocolate lovers.
Let cool completely before storing between sheets of waxed paper in an airtight container for up to a week.