In honour of Pi Day, I created the Whoopie Pi. Now you can make some too, with the help of this Instructable!

Step 1: Spiced Rum Whoopie Pie Recipe.

First, make some whoopie pie batter. Mine are spiced rum flavour, and can be made as follows...

Cream 110g butter with 180g caster sugar. Add two eggs, one at a time, and then add 75ml milk and 30ml rum. Mix well.

Add 1 tsp each of mixed spice and ground ginger, plus a pinch of salt and 250g gluten free self raising flour mix. That's right - they're gluten free, too!

Step 2:

Fold the dry ingredients into the mix with a spatula. You want the batter to be thick enough to hold a shape, but not so thick that it can't be pushed through a piping bag without damaging the bag or yourself.

Step 3: Shape the Whoopie Pi

Fit a piping bag with a rectangular or petal tip nozzle - it looks a little like a calligraphy pen. Perfect for making that Pi shape. Draw as many as your batter will make - this depends on the size you go for. I preferred the smaller ones, though it's hard to keep them all
even.

Start with the top bar, this is the easiest part. Keeping the nozzle close to the paper will help to control the shape. Don't be afraid to go back and double over any parts that look like they need thickened up a little, especially around the joins, or to use a teaspoon to reshape any bits that haven't come out right.

Make sure to leave space between them and make the lines thin enough so that they won't touch even after they puff up in the oven. Also remember to pipe half facing backwards, so that you can pair them up.

Step 4:

Bake at 170C for eight minutes, rotating half way through. Slide the baking paper off the baking sheets, then replace with fresh paper and pipe more shapes. While the second batch bakes, remove the first ones from their paper. My method is to hold the edge of the paper between finger and thumb, then use the back of the fingernails on the same hand to push the cake away from the paper, instead of peeling the paper away from the cake. Some will get broken, no matter what you do. That is OK, you did your best.

Step 5:

Match up similarly sized Pi shapes, and sandwich them together with your favourite buttercream or jam. Whipped cream also works if you're going to eat them soon. Mine are sandwiched with a lemon-sesame buttercream.

When handling the shapes, take care to hold them by the top bar and be gentle. Don't lift them in such a way as to press the two 'legs' together, this will cause stress and possible breaking. The weakest points are the joins between top bar and vertical legs, be wary of them, or suffer the consequences.

Applying the filling is best done by holding one pi flat on your hand, and using a piping bag to pipe the filling on top. You can also use a teaspoon - keep the spoon full and use the bowl to spread the filling, it's more forgiving than spreading with the back of the spoon. Lightly press the other pie on top when you're done - the filling should stick them together without too much pressure.