Double Chocolate Tart with Blackberries

1 Preheat the oven to 200 ºC or 390 ºF.
2 In a bowl, combine the softened butter with flour. Use your hands or a food processor for mixing. Add an egg. Mixing the ingredients together shouldn't take more than 5 minutes.
3 Take a baking form (mine is 24 cm or 9 inches in diameter) and sprinkle the dough over the bottom. Press firmly with your fingers and distribute evenly to the bottom and sides (sides shouldn't be lower than 3 cm or 1 inch).
4 Put the form in the fridge for 20 minutes or in the freezer for 10 minutes.
5 Make the filling: Use a water bath for melting. In a pot, boil a small amount of water over medium heat and put a heatproof bowl or pot in the water. Break the chocolate into pieces and stir them in the pot. Add cream and butter. Wait until the mixture is homogeneous, stirring occasionally. Remove from the heat.
6 Put the form into the oven for 10 minutes.
7 Loosely beat the eggs and stir them in the chocolate mixture.
8 When the crust turns golden, pour the chocolate mixture on it and put it in the oven for 15 minutes.
9 Prepare the cream: whip it for 8 minutes with beaters or an immersion blender. Add sugar and cocoa powder and whip for 1 more minute.
10 Let the tart cool down for at least 1 hour. Arrange blackberries around the rim and cover the tart with cream. You can use a spatula or a culinary syringe, like the one from the link above. Optional: sprinkle with cocoa power.
11 You can refrigerate this tart for at least 2 days.
12 Enjoy!