Make the macarons. Line two large baking sheets with baking parchment. Draw 12 8cm circles on the parchment, spacing well apart. Flip so the ink is underneath.
Pulse the almonds and icing sugar in a food processor until fine. Pass through a fine sieve and discard any large lumps that won’t go through. Stir through 2 egg whites to make a thick paste, then set aside.
Heat the granulated sugar and 100ml water in a small pan over low heat until the sugar dissolves. Turn up heat and bubble until mixture reaches 115°C on a sugar thermometer. Meanwhile, beat the remaining egg whites in a freestanding mixer to soft peaks. When the sugar mixture reaches 115°C,
slowly and steadily pour into the egg whites, with the mixer still running. Continue to beat for around 10min, until the outside of the bowl is just warm to touch. Gently fold into the almond paste.
Spoon mixture into a piping bag fitted with a 1cm nozzle and pipe inside the circles. Leave to rest for 30mins, or until the macarons have formed a skin. Preheat oven to 170°C (150°C fan) mark 3.
Bake the macarons for 25min, or until they easily peel away from the parchment. Cool completely on the trays.
Meanwhile, make the ice cream filling. Heat the blackberries, sugar and 2tbsp water in a pan over low heat, stirring until the sugar has dissolved. Turn up heat to medium and bubble for 10min, or until the blackberries are mushy and the mixture is thick and syrupy. Remove from heat and pass through a fine sieve, discarding the seedy pulp.
Decant the ice cream into a large bowl and ripple through the cooled syrup. Pour into a deep roasting tin, approx 20 x 25cm, lined with baking parchment. Freeze for at least 4hr, or until solid. Once frozen, cut out 6 circles of the ice cream using an 8cm round cutter. Put onto a lined baking tray and freeze again for 2hr, or until solid. Sandwich each disc between 2 macarons to serve.