Follow these steps to craft your own brownie cookie sandwiches with cookie dough buttercream:

1. Prep the Flour

• Preheat your oven to 300°F (150°C).
• Spread 1/2 cup of flour on a baking sheet and bake for 5-8 minutes until it reaches 165°F to ensure it’s safe to use raw. Let it cool.

2. Make Brownie Cookies

• Melt the butter and chocolate chips together in a bowl over simmering water. Stir until smooth and let it cool slightly.
• In a separate bowl, mix flour, cocoa powder, baking powder, baking soda, and salt.
• Whisk the eggs, granulated sugar, brown sugar, and vanilla extract into the cooled chocolate mixture. Gradually add the dry ingredients until combined.
• Chill the dough for 30 minutes to make it easier to handle.

3. Bake Cookies

• Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
• Scoop tablespoon-sized balls of dough onto the sheets, spacing them apart.
• Bake for 8-10 minutes until the edges are set. Let them cool on wire racks.

4. Make Buttercream

• Beat the softened butter and brown sugar until fluffy. Gradually mix in the powdered sugar and flour.
• Add the vanilla extract and milk one tablespoon at a time until you reach the desired consistency.

5. Assemble Sandwiches

• Pipe or spread the buttercream onto the flat side of one cookie, then press another cookie on top. Enjoy your creation!