Preheat oven to 350 degrees F. Line a 9"x9" square baking pan with 2 pieces of foil (foil needs to be large enough to hang over the sides), then grease the foil with butter or nonstick cooking spray. Set aside.

Whisk together the flour, salt and baking powder in a small mixing bowl. Set aside.

Melt the butter, chocolate and cocoa powder in a large-sized saucepan/dutch oven over medium-low heat, stirring constantly until smooth and completely combined/melted. Do not let the chocolate scorch on the bottom of the pan because scorched chocolate does not taste good.

Once everything is melted together, remove the pan from the heat and stir in the sugar.
Note: The mixture will be grainy. It's ok, it's supposed to be like this.*

Stir in the eggs and vanilla, stirring quickly to prevent the eggs from cooking, then gently stir in the dry ingredients, mixing just until incorporated (do not over-mix).

Pour into the prepared pan, spread evenly and bake in the preheated oven for 25-30 minutes or until toothpick inserted into the center comes out almost completely clean. (I find brownies to be fickle and the cooking time tends to vary from oven to oven, so start watching them after the 25 minute mark).
*These brownies taste best when they are not over-baked. For me, they are always done exactly at the 25 minute mark.*

Remove from oven and allow to cool completely. While the brownies are cooling, make the chocolate raspberry mousse.

Begin by making cream cheese frosting. Cream the butter and cream cheese together in a small mixing bowl, using an electric handheld mixer.

Slowly add in the powdered sugar, mixing on low speed, until smooth and creamy (depending on how packed in your sugar was in the measuring cup, you may need slightly less or more than 2 cups. Add it in slowly so you can stop when it gets to the right consistency). Add in the vanilla and mix until thoroughly combined and frosting is smooth and creamy.

Set aside 1 cup of the frosting to be used for the mousse (there will be a little bit more than that).

In a medium-sized saucepan over medium-low to medium heat, melt the chocolate chips with the whipping cream/heavy cream and the raspberry preserves/jam/jelly, stirring constantly. Once the chocolate is completely melted, add in the raspberry extract, stirring to thoroughly mix in, then set the saucepan in the refrigerator for about 30 minutes for the mixture to cool enough so it thickens up.

Once the chocolate raspberry mixture has thickened, remove from the refrigerator and transfer to a medium-sized mixing bowl. Add in the 1 cup of reserved cream cheese frosting and then beat on high speed using an electric mixer for about a minute or so until the mousse is thoroughly blended and fluffy.

Spread the mousse over top of the cooled brownies and spread out evenly over the top.

Place the reserved 2 Tbsp. of chocolate chips and 2 tsp. of heavy cream/whipping cream in a small microwavable dish. Heat on 50% power in 15 second intervals, stirring after each interval, until the chocolate melts completely and the mixture is completely smooth. If the mixture is too thick, add a tiny bit more heavy cream/whipping cream and heat about another 5 seconds, then stir until thoroughly combined.

Drizzle over top of the mousse. I placed the chocolate mixture into a small ziploc bag, then cut off a small hole in one of the bottom corners and used that to drizzle over the top.

Loosely cover the brownie pan (try to avoid the cover sinking down into the top of the brownies, as you will lose some of the chocolate drizzle when you remove the top) and refrigerate for at least 1 hour (closer to 2 is best) until the mousse is completely set/firm (if you cut into these too soon, it will be very messy as the mousse is super soft at room temperature).

Once the brownies have thoroughly chilled and mousse is set, remove from the refrigerator and then lift the brownies out of the pan using the sides of the foil to lift up.

Peel the foil down from the sides of the brownies, then cut. *Note: I recommend running the knife under fairly hot water and wiping off before/after each cut, as this makes it much easier to cut through in even, pretty lines.*

Serve brownies straight from the refrigerator or after sitting out at room temperature for about 20 minutes (straight from the fridge the mousse is a bit thicker and obviously the brownies are cold. After sitting out a bit, the mousse is much softer and they are no longer cold. I don't recommend microwaving these brownies, as the mousse will melt off if heated too long).

Store brownies in an air-tight container in the refrigerator.