Peanut Butter Dulce de Leche Cookies

Place butter and salt in a large bowl. Using an electric mixer, beat on medium-high speed until butter is very creamy. Add sugar; continue to beat until very light and fluffy, scraping down sides, about 2 minutes. Beat in egg yolk and vanilla.

In a separate bowl, stir flour with powdered peanut butter. On low speed, beat flour mixture into butter mixture, just until blended. If easier, use a spoon or your hands to mix near the end. Using floured hands, remove from bowl and divide into 2 balls. Flatten each ball into a round disc, about ½ inch (1 cm) thick. Wrap in plastic wrap and refrigerate for at least an hour.

When ready to bake, preheat oven to 350°F (180°C). Line a large baking sheet with parchment paper. Remove one disc of dough from refrigerator to work with at a time. Dough will take 10 to 12 minutes resting at room temperature before you can roll it. Dust counter and rolling pin with flour. Roll out dough to about ¼ inch (0.5 cm) thick. Using a 2-inch (5-cm) round cookie cutter, cut out circles and place on baking sheet about 2 inches (5 cm) apart. Gently press a peanut onto half of the cookies. Bake in centre of preheated oven, until golden around edges and baked through, about 10 minutes. Transfer to a rack to cool completely.

Gather dough scraps, form into a disc and refrigerate. Repeat, rolling remaining disc and scraps, topping half the cookies with remaining peanuts. Make sure baking sheet is cool before placing dough circles on it.

Once cookies are completely cool, sandwich 1 peanut-topped cookie with a plain cookie using about 1 heaping teaspoon (7 mL) dulce de leche. Dust top with icing sugar. Repeat with remaining cookies. Store in an airtight container for up to 3 days, or freeze.