1.  To prepare basil buttercream, combine basil leaves, milk, and half-and-half in medium saucepan. Heat gently over medium heat until just simmering, then remove from heat. Let cool and then refrigerate at least 2 hours and up to overnight. Remove basil leaves from the cream, then squeeze the leaves over the cream. Discard leaves.

2.  In medium bowl, whisk together sugar, flour, and salt really well (the sugar will help keep the flour from lumping when it boils, so spend a good minute really whisking it together). Place mixture in medium, heavy-bottom saucepan. Slowly pour the basil cream into the flour, whisking to combine as you pour. Cook over medium heat, stirring constantly with a whisk, until the mixture comes to a gentle boil (periodically run a spatula round the edges of the saucepan to remove any flour lurking there). Reduce heat slightly, and continue to whisk until the mixture has thickened considerably, 2 to 3 minutes. Remove from heat and continue stirring 30 seconds.

3.  Transfer mixture to a bowl and cover with plastic wrap, making sure the plastic sits directly on the surface (this will help keep it from forming a skin). Let cool to room temperature.

4.  Meanwhile, prepare brownies. Adjust oven rack to middle of oven. Preheat oven to 350F. Grease a 9x13 inch baking pan and line with a parchment sling. 

5.  In small bowl, whisk together flour, salt, and baking powder. 

6.  In large bowl, whisk together eggs, granulated and brown sugars, canola oil, and vanilla.

7.  Place butter and chocolate in small, heavy-bottom saucepan set over low heat and melt together, stirring frequently to prevent chocolate from scorching. Continue cooking until mixture is smooth. Off the heat, add cocoa powder and whisk until completely combined. 

8.  Add chocolate mixture to sugar-egg mixture and whisk until smooth. Add flour mixture and stir with a spatula until just combined. Pour batter into prepared pan and bake 22-27 minutes, until sides of brownies have set, the top starts to crackle and look glossy, and a toothpick inserted into the center comes out with crumbs. The batter on the toothpick should not be wet but should have a good amount of crumbs clinging to it. Transfer pan to wire rack and let cool completely. Chill once cooled if you like. 

9.  When basil cream mixture has cooled, place butter in the bowl of a stand mixer fitted with a paddle, and beat on medium speed until smooth and creamy, scraping down the sides as needed. Start adding flour mixture a few spoonfuls at a time, mixing on low speed after each addition, until it is all incorporated. Scrape down the sides and mix on medium speed until the buttercream is light and fluffy, 2 to 3 minutes. Add vanilla and food coloring, if using, and mix on low speed until combined.

10.  To prepare ganache, place chocolate in small bowl. Heat heavy cream in small saucepan until simmering and just about to boil. Pour cream over the chocolate, cover the bowl with plastic wrap, and let sit for 5 minutes. Remove the plastic and whisk until completely smooth. Let cool to room temperature.

11.  Spread the basil buttercream evenly on top of cooled or chilled brownies. Return the pan to the refrigerator and chill for 1 hour. Pour the cooled ganache over the top of the chilled buttercream and, using an offset spatula, spread it in an even layer. Return the pan to the refrigerator for 1 hour.

12.  Remove pan from the refrigerator and let sit for 10 minutes before cutting, to allow the glaze to soften slightly. Cut into bars and serve. Store brownies in an airtight container in the refrigerator for up to 3 days.

Reprinted from 100 Cookies by Sarah Kieffer with permission by Chronicle Books, 2020.