Cream butter and sugar together until light and fluffy. Beat in egg, then vanilla.
In a separate bowl, whisk together flour, cocoa and salt; add to butter mixture and beat to combine. Transfer dough to refrigerator to chill for 1 hour (or you may refrigerate the dough for up to 2 days before baking).
While dough is chilling, prepare filling. Heat whipping cream to a simmer in the microwave (about 1 1/2 minutes on high power). Pour over chocolate, and whisk until smooth. Cool in refrigerator.
Preheat oven to 350 degrees F. Working with one half of the dough at a time, form a disc then roll it out to 1/4 inch thickness between two sheets of waxed or parchment paper. Use a 2-inch heart shaped cookie cutter to cut out shapes; transfer to baking sheets.
Decorate cookies with coloured sugar or sprinkles, if desired. Bake one sheet at a time for 9-11 minutes, until cookies are firm. Cool 2 minutes on sheet before transferring to wire racks.
Once cookies have cooled completely, spread half of them with about 2 teaspoons of filling and top with the remaining half. Cookies may be stored in the refrigerator for 3 days, or frozen up to 1 month.
Baker’s Tip: be sure to roll the dough out between two sheets of waxed or parchment paper, for ease of handling. That way, if at any point you find the dough sticky, or if you have difficulty maintaining the shape while lifting the hearts, simply transfer the sheet of dough on the waxed paper to the freezer to firm up for 2 minutes before continuing.
Per Chocolate Fudge Sandwich Cookies
nutrition information per cookie sandwich: 267 calories, 15 g fat, 9 g saturated fat, 46 mg cholesterol, 148 mg sodium, 34 g carbohydrate, 2 g fibre, 21 g sugars, 3 g protein