To PREPARE BROWNIES you need to preheat the oven to 325 F, first.

Next, you should line 9 x 13 inch baking pan with parchment paper and set aside. Combine flour, cocoa, salt and baking powder in a medium dish and set aside.

Then, beat eggs using high speed until they are light and fluffy and add sugar and beat some more until well combined.

After that, fold in melted butter and vanilla and beat them until all the ingredients are well combined. Add dry ingredients and beat at low speed, be careful not to over mix it.

Then, put the barter in a baking pan and bake for 40 minutes, or until the toothpick comes out with some moist crumbs on it.

You should take it out of the oven to cool.

TO PREPARE BAILEYS CHOCOLATE MOUSSE, you need to put gelatin and cold water into a small dish and mix then leave it for 1 minute.

After that, add hot water and stir until gelatin melts completely and leave it to cool.

Next, combine sugar and cocoa, add heavy cream and beat until
stiff peaks form. Continue beating slowly adding Bailey´s and vanilla and
finally, cooled gelatin. 

Beat until soft peaks form and then leave for a couple of minutes. When brownies are cool, take them out of the baking pan, remove parchment paper and spread Baileys Chocolate Mousse on the top.

Next, melt chocolate, add oil and stir, then drizzle over Baileys Chocolate Mousse.