For the pastry, combine the flour, butter, coffee flour and sugar in a food processor and blitz until it resembles fine breadcrumbs. Add egg yolk and water and blitz to combine. Turn out of the food processor onto a bench and bring dough together. Wrap with plastic wrap and set aside in the fridge to rest for 30 minutes.
Remove pastry from fridge. Cut into 4 pieces and roll each piece out. Line 4 x 10.5cm tart tins and prick the base of the tart with a fork. Place in freezer for 5 minutes. Cover with baking paper, fill with baking beans and blind bake pastry until golden brown, about 15 to 20 minutes. Set aside to cool.
For the curd, whisk egg yolks and flour together. Combine zest, sugar and butter in a small saucepan and gently heat, dissolving the sugar. Pour the mixture into the egg yolk and flour, stirring continuously. Transfer mix to a small pan and return to a gentle heat, stirring continuously until the mixture thickens, about 2 minutes. Remove from heat and transfer to a bowl. Cover and set aside in the fridge to cool.
For the ant praline, place ants on a lined baking tray. Place sugar in a pan and heat to a caramel colour. Once golden, pour over the ants and set aside in the fridge to set. Once set, break praline into small pieces and set aside.
To make the filling, whip the cream with the sugar and transfer to a piping bag. Set aside.
To assemble, remove pastry shell from the tart tin. Divide curd between tart shells. Place acha-cha on top of the curd and pipe sweetened cream over the top. Sprinkle with ant praline and garnish with extra sweetened cream.