To prepare the bars:

1. Preheat the oven to 325 degrees and line an 8 or 9” square baking pan with foil. Lightly grease with cooking spray and set aside.
2. Begin by preparing the crust. In a large bowl or the bowl of a stand mixer, cream the butter and granulated sugar until smooth. Stir in the vanilla bean paste. Add the flour and salt and stir just until combined to crumbs. Gently press the mixture down flat into the bottom of the prepared pan and bake in the preheated oven for 20 minutes until set. In the meantime, begin making the brownie filling.
3. In a medium saucepan over low heat, gently melt together the butter, chocolate chips, and sugar, stirring regularly to melt evenly and prevent scorching the chocolate. Once melted and smooth, set aside. 
4. In a large bowl, beat the eggs on medium speed with a mixer until they lighten in color and fluff up, about 2-3 minutes. Gently stir in the chocolate mixture. Add the flour, cocoa powder, baking powder, and salt, stirring just until combined. Pour the batter on top of the prepared shortbread and smooth. Increase the oven heat to 350 and bake for an additional 30-33 minutes or until a toothpick inserted into the middle comes out only with a couple of small brownie crumbs. Do not overbake. Remove from oven and allow to cool completely prior to slicing.