In a measuring cup add warm milk and yeast together. Stir together to combine, then allow to sit until it becomes foamy, about 10 minutes. Meanwhile, in a medium mixing bowl, add egg, yolk, salt, vanilla, and sugar. Whisk together to combine.

Add egg mixture, foamy yeast-milk, and flour to stand mixer. Using a large wooden spoon, mix together the dough until a shaggy dough forms. Place the dough hook onto the stand mixer and turn the stand mixer onto medium. Beat the dough until it has come together and looks uniform.

While still beating the dough, begin adding in the butter 1 tbsp at a time, ensuring that each addition is incorporated before adding the next. After all the butter has been added, continue to beat for another 5-8 minutes, or until the dough is smooth, elastic, and tacky.

Transfer dough to a greased large bowl, cover with plastic wrap, then place in a warm area to rise for about an hour, or until the dough is doubled in size.

Place a heat proof bowl over top of a small saucepan of simmering water. Add both chocolates and butter to the heatproof bowl. Heat until the chocolate has just melted and is combined with the butter. Remove from heat and add in cocoa powder and brown sugar. Stir to dissolve. The consistency should be a paste like consistency.

Prepare a 9”x5” loaf pan with grease and parchment paper. Turn the dough out onto a lightly flour work surface, and roll the dough out into a 15”x15” square.

Spread chocolate ganache over top of the dough, leaving about a 1” strip along the top. Sprinkle graham cracker crumbs and mini marshmallows over top. Brush the bare 1” strip with a bit of water. Roll the dough away from you into a log (try to maintain even thickness throughout).

Using a serrated knife, slice the log in half lengthwise. Place the sliced halves face up and side by side each other. Form an ‘X’ formation with the two strips. Working from center out, interweave the two strips by folding them over one another alternating back and forth. When at the end, pinch the ends together. Repeat on the other half.

Add graham crackers to food processor and pulse until they become fine in texture. Add brown sugar and salt, pulse to combine. Then add cold butter pieces, and pulse until crumbly.

Preheat oven to 375°F. After the dough has doubled in size, place into the oven and bake for about 20 minutes, then sprinkle streusel on, then bake for another 15 minutes (internal temperature of 200°F). When done, allow to cool in pan for 15 minutes, then transfer to a cooling rack and allow to cool completely before cutting into it.