In a mixer, using the paddle attachment, combine the butter and sugar, beat until cream, then add the egg one by one. Then add cold milk to the mixture.
Add the flour and just beat until incorporated, wrap the dough in plastic wrap and refrigerate for approximately 2 hours until firm.
Pre-heat oven to 175 degrees Celcius, line a sheet pan with parchment paper, place 7cm diameter flan rings on the lined sheet pan. Roll the sugar dough out to a thickness of 0.16cm and line the flan rings with the dough. Bake until light golden brown (approx. 10 minutes.) Remove from oven and let cool completely.
Choc Tart Filling
Pre-heat oven to 175C. Place the chopped chocolates in a heat proof bowl. Combine the butter and sugar in a sauce pan and heat until the sugar has completely dissolved. Pour the hot butter mixture over the choc. Stir gently to combine.
Whisk the eggs together and gently whisk all into the chocolate mixture.
Pour the mixture into the pre-baked shells and re-bake about 10 to 11 minutes till set. Remove from oven and let cool completely before serving.