Pulse the ground almonds long with the icing sugar, paprika and chilli powder. Sieve the mixture a couple of times. Keep aside.
In a clean, dry bowl, add the egg white and beat with an electric whisk till it forms soft peaks.
Gradually add the granulated sugar and beat till it forms stiff peaks.
Add the dry mixture to the egg white mixture a little at a time. Use a flexible spatula in a circular movement and press against the edges of the bowl. When everything is mixed well, the mixture should fall down in ribbons when lifted with the spatula.
Line a baking tray with parchment.
Transfer the mixture to a piping bag and snip the end.
Pipe the macaron batter out into circles of about 1½ in diameter, a little apart from each other. If you are okay with free hand piping, this will be a breeze. If you are not, you can draw circles on the backside of the piece of parchment paper that you will use to line the baking tray. This will help to get uniform sizes. Once the circles of macaron batter have been piped out, tap the tray gently on the counter to smoothen the tops and release any air bubbles.
Sprinkle a little crushed red chillies on top of half of the piped shells.
Leave them to stand at room temperature for about 45 minutes. The tops should feel dry to the touch.
Pre heat the oven at 170 deg C.
Lower the temperature to 150 deg C and place the tray in the centre of the oven.
Bake for 15 minutes.
Rotate the tray and bake for another 7 minutes.
Cool the macarons on the tray for a couple of minutes. Remove and transfer to a rack to cool completely.
Just before serving, sandwich each plain shell with the ones topped with crushed red chillies with some of the sour cream filling.