Preheat oven to 360 degrees F/ 180 degrees C. Grease very well a 9 x 7 inch/ 23 x 20 cm baking dish or similar.
In a large bowl beat together butter and sugar with an electric mixer for about 1 minute. Add eggs and beat very well until smooth. Add lemon zest and beat until just absorbed. Using a rubber spatula gradually fold the flour into the mixture.
Pour the batter into the prepared pan and bake for about 25 minutes or until a toothpick inserted in the center comes out clean.
Let cool for 5 minutes and spread the glaze on top. Serve after it cools down for another 15 minutes.
Melt the chocolate in a double boiler or in the microwave at the lowest power.
Pass the lemon juice through a fine sieve and then mix it with the chocolate until smooth.
Distribute the glaze evenly with a spatula.
I normally use store bough dried lemon zest. In this case you can use about 1-2 teaspoons. For even more intensive lemon taste you can add also some lemon extract to the brownie batter.
Store the leftover lemon brownies in airtight container in the fridge or covered with plastic wrap.