To prepare a lemon curd:
Mix yolks with sugar and starch. Add lemon juice.
Put the pan with egg-lemon mass on medium heat and cook, stirring all the time for 4-5 minutes or until the cream thickens.
Add the cream butter, mix well and leave the cream to cool
Melt the chocolate with butter (in a water bath or micro).
Beat the eggs with sugar (2-3 min) until fluffy.
Add chocolate to the egg mixture and mix.
Mix the flour with cocoa and salt and add to the chocolate mass. Gently mix with a spoon (stir until smooth dough, no more) Put the mass in the pan covered with baking paper.
On top lay a curd.
To make a "marble": Gently barbecue with a stick or knife edge mix both masses (preferably chocolate, almost completely covered curd).
Put bake in a preheated oven to 170 degrees (brownie is ready when a toothpick, stuck in the middle of the pie, "come out" from there wet, but not wet).
Remove the brownies from the oven, allow to cool at room temperature, and then put the brownies in the freezer for 2-3 hours (this is done to make the brownies better frozen and easier to cut).
Remove the brownies from the freezer, cut into squares and.. enjoy your meal:)
In the original recipe baking time is written 25 minutes.. I usually have so much brownie and bake, but here after 25 minutes, the cake was almost liquid and only after 40 minutes, I got the desired consistency of the cake.. So, focus on your oven.. Maybe 25 minutes is enough for you.