Preheat oven to 350F/180C.
Using a heavy-duty stand mixer, cream the butter and sugars until light and fluffy.
Add the egg and vanilla, mixing well.
Mix all the dry ingredients in a large bowl. Add gradually to the butter mixture, mixing well.
Add the heavy cream and mix just until incorporated. Add the dough to pastry bag. I used s very large star tip, but a plain round one about 1/2-inch/1.25-cm will do just as well.
Line baking sheets with parchment and pipe dough about 3-inches/7.5-cm long and about 2-inches/5-cm apart.
Bake for 14-16 minutes or until cookies are just beginning to get golden around the edges. Let the cookies cool on the sheet until firm enough to move to cooling racks.
To fill and decorate: Melt chocolate morsels in the microwave for 45 seconds; stir until smooth. They may need 10-15 seconds more if they're not completely melted.
Spread about 1 tablespoon of jam on flat bottom of one cookie. Top with the flat side of a plain cookie.
Dip the tip of each sandwich cookie in the melted chocolate then dip the chocolate part in the sprinkles.
Amount of cookies will vary with how big you want to make them. I got around 1 1/2 dozen sandwiches.