Donna Hay's recipe instructs the cook to make caramel by cooking sweetened condensed milk with butter and golden syrup (a common product in the UK and Australia -- if you can't find it in the US, substitute brown-sugar-flavored corn syrup) until "thick." According to the recipe, this will take 15 to 20 minutes. I cooked the mixture over boiling water for 20 minutes without noticing any appreciable thickening. After about 30 minutes, it began to look somewhat thicker, and after 45 minutes, it seemed to be as thick as it was going to get. Even so, the consistency seemed rather loose to serve as filling for cookies; I cooled the caramel for 10 minutes, as instructed in the recipe, but this didn't help it to get any thicker. As a test, I went ahead and filled a couple of cookies with the caramel, but as I feared, the loose texture caused the top cookie to slide right off the bottom cookie, and the caramel all dripped out onto the countertop. These weren't sandwiches, really...more like half-frosted lopsided cookie towers. I put the caramel in the refrigerator to get truly firm, and after about 30 minutes it finally seemed like it might be set up enough to use with the cookies.

I had to be careful not to push the two cookies together too tightly, however, since doing so caused the caramel to leak out from the center of the sandwich. A gentle touch produced sandwiches that held together without becoming a leaky mess.

Be sure to use only 1 Tbsp of dough for each cookie; you don't want them to be too big. The original recipe is vague about spacing the cookies on the baking sheet. I recommend that you place the cookies about 2 inches apart. They don't spread a great deal in the oven, but you don't want them so close that they'll touch.

Prep Time: 20 minutes
Cook Time: about 45 minutes
Yield: 2 dozen sandwiches

8 oz. butter, chopped
1 cup confectioner's sugar
1 1/2 cups all-purpose flour, sifted
1 cup cornstarch, sifted
1 egg

14-oz. can sweetened condensed milk
4 Tbsp butter
2 Tbsp golden syrup or brown sugar corn syrup

Preheat the oven to 350 degrees.

Place the butter, sugar, flour, cornstarch, and egg in a food processor and process until a smooth dough forms. Roll tablespoons of the dough into balls and place about 2 inches apart on cookie sheets lined with parchment paper. Flatten the balls slightly with the bottom of a drinking glass, or your hands. Chill about 10 minutes, or until firm. Bake until lightly golden, about 12 to 15 minutes. Cool the cookies on racks.

For the caramel filling: Combine the condensed milk, butter, and syrup in a heatproof bowl. Place the bowl over a saucepan of boiling water and cook, stirring occasionally, until the mixture has thickened, about 45 minutes. Cool the caramel in the refrigerator, stirring every 10 minutes, until cool enough to touch, about 30 minutes.

To fill the cookies: spoon about 2 tsp of caramel filling onto the flat side of 1 biscuit. Top with another biscuit and allow the cookies to cool completely before serving.