FOR THE TOP CHOCOLATE LAYER (GLAZE)
Line a 8x8 baking pan with foil, leaving an overhang on the sides; set aside.
In a saucepan, combine water, sugar, and butter; place over medium heat and stir occasionally until the sugar dissolves and butter melts.
Stir in the ground crackers and hazelnuts; stir mixture until completely combined.
Remove from heat and stir in vanilla.
Divide batter into two equal parts.
Pour melted chocolate into one of the batters.
Transfer only HALF of the chocolate batter to previously prepared pan.
Place in freezer for 15 to 20 minutes, or until it sets.
Spread the light-colored batter over the chocolate batter; freeze for 15 minutes or until it sets.
Add the remaining chocolate batter over the top; place in freezer for 15 minutes, or until set.
In the meantime, prepare the top chocolate layer.
Combine milk, powdered sugar and butter in a saucepan; cook and stir over medium-high heat until butter melts.
Remove from heat; add chocolate, and stir until chocolate melts.
Spread chocolate mixture evenly over bajadera.
Refrigerate at least 4 hours, or overnight.
Sprinkle with sea salt.
Using the overhang as handles, remove bajadera from pan; using a sharp knife, cut into 24 bars.