First prepare your 8" springform pan with parchment paper lining and a spray of pan spray
Preheat the oven to 350°F and prepare the brownie recipe as per the instructions on that post but you will bake it in an 8" springform pan
Once the brownie is completely cooled
Prepare the chocolate mousse by bringing the cashews to a rolling boil in approximately 1½ cups of water
Turn off the heat and let them soak for 30 minutes, then drain & rinse
Combine the warm cashews and room temperature Irish Cream together in a high speed blender and blend smooth
Melt the vegan chocolate in a large bowl then add the warm cashew/Irish Cream mixture and whisk smooth
Whip the vegan whipped cream to medium peaks then fold into the chocolate base only if the chocolate mixture is cool to the touch or you will melt the cream
Pour the Irish Cream Chocolate Mousse into the springform pan on top of the brownie base and then refrigerate until set approximately 3 hours or overnight
Prepare the Irish Cream Ganache by combining all the ingredients for the ganache in a small sauce pot and heat over low-medium heat whisking constantly until melted & smooth
Pour the warm ganache over the set mousse cake and refrigerate again to set completely
Meanwhile prepare the Irish Cream buttercream by whipping the room temperature vegan butter with the salt until fluffy with the paddle attachment of an electric stand mixer
Add the sifted confectioners sugar and mix smooth
Once all the sugar is incorporated, scrape the bottom & sides of the bowl and whip on high for 3 minutes
On low speed slowly add the Irish Cream 1 Tbs at a time until it is all incorporated
Pipe the buttercream onto the mousse cake as shown in the video tutorial
Use the excess ganache for a drizzle on each slice