Add the graham crackers and pretzels to a food processor, process until finely ground. Add the melted butter, process until well combined. Press into the bottom of a 9x13 pan (or use a 7x11 for thicker bars) until well compacted.
Bake for 12 minutes.
Make the fudge:
Add the chocolate, sweetened condensed milk, vanilla extract, beer and salt to the top of a double boiler (or a metal bowl set over a pot of gently simmering water).
Stir over medium-low heat (make sure the water does not boil) until most of the chocolate has melted. Remove from heat, continue to stir until all the chocolate has melted.
Pour over the crust, refrigerate until set, about 30 minutes.
Make the marshmallow layer:
Add the egg white and cream of tartar to a stand mixer fitted with a whisk attachment, beat until light and foamy.
Add 1 tablespoon sugar and beat until stiff peaks form
In a saucepan, add the water (or beer), agave, and 1/3 cup sugar.
Cook over medium heat while stirring until the mixture reaches 248°F on a candy thermometer. This will take about 6-8 minutes.
Once the corn syrup mixture is ready, turn the mixer on medium and in a slow steady stream, pour the corn syrup mixture into the beaten egg whites.
Once all of the corn syrup mixture has been added, beat on high for 5 minutes until the mixture is stiff and glossy.
Add vanilla extract and beat on high 1 minute.
Spread over the fudge in an even layer. Chill until ready to set, about 15 minutes.Brulee with top with a kitchen torch, or place under the broiler until browned.
Cut into squares, chill until ready to serve.
Yes, you CAN use Marshmallow Fluff instead. But it needs to be kept refridgerated or it will slide all over the place.