In a medium saucepan, combine whole milk, granulated sugar, the scraped seeds and pod of a vanilla bean, and a pinch of salt. Heat over medium until steaming but not boiling, about 5 minutes. Remove from heat and stir in the heavy cream. Let the mixture cool before transferring it to the fridge to chill for at least 2 hours.

Once the ice cream mixture is thoroughly chilled, pour it into your ice cream maker according to the manufacturer's instructions. Churn until it achieves a soft-serve consistency, typically 20-30 minutes. Transfer the ice cream to a lined baking pan, smoothing the top, and freeze for several hours until firm.

While the ice cream firms up, preheat your oven to 350°F (175°C). Prepare two baking sheets by lining them with parchment paper.

In a mixing bowl, cream together softened unsalted butter, brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes. Beat in the large eggs and vanilla extract until well combined. Gradually sift in all-purpose flour, unsweetened cocoa powder, instant espresso powder, baking soda, and salt, mixing until just combined to form a smooth dough.

On a lightly floured surface or between sheets of parchment paper, roll out the cookie dough to about 1/4 inch thick. Use a round cookie cutter to cut out cookie shapes and place them on the prepared baking sheets.

Bake the cookies in the preheated oven for 10-12 minutes, or until the edges are firm and the centers slightly soft. Allow the cookies to cool on the pans for about 5 minutes before transferring them to a wire rack.

Once the ice cream is firm, remove it from the freezer and cut it into rounds using a cookie cutter. Take one cookie, place a round of ice cream on top, then cover with another cookie to create your Vanilla Bean Frappuccino Sandwich. Wrap each assembled sandwich in parchment paper.

Place the wrapped sandwiches back into the freezer for at least one hour to set. Enjoy your delicious homemade Vanilla Bean Frappuccino Sandwiches on a warm day!