The Bottom Less Pit

Dough
In the bowl of a stand mixer add in the flour, sugar, and yeast, then whisk to combine. 
Add in the warm milk, butter, egg, lemon zest and vanilla.
Use the dough hook attachment to knead the dough on medium low speed until smooth and the sides of the mixing bowl are clean.
Shape the dough into a ball and place in a lightly greased bowl, cover with a lid or plastic and place somewhere warm to rise for 45 minutes. 
Preheat the oven to 350 F and arrange two racks so that they divide the oven into thirds. 

Streusel
The streusel is optional but I think it adds so much to them!
In a medium bowl whisk together the flour and sugar. Then add in the butter and vanilla.
Rub the butter into the dry ingredients using a fork until all of the butter has been fully mixed in.

Assemble
Line two baking sheets with parchment paper or silicone baking mats. 
Once doubled in size, lightly sprinkle the dough with flour and punch out the air from the dough.
Lightly flour your work surface and pat the dough into a skinny rectangle. 
Gently roll the dough out to approximately 20 cm x 45 cm. I recommend rolling the short end closest to you a little thinner so the center isn't too thick.
Spoon 200 grams of the jam over the surface of the rolled out dough and use an offset spatula or a rubber spatula to spread the jam over the whole surface of the dough, all the way to the edges.
Starting with the short side closest to you, roll the dough up tight but not too tight that all of the jam squeezes out.
Use a knife and ruler to mark the roll into approximately, 1" slices.
Use the same sharp knife to cut the roll into slices.
Lay half of the slices onto each lined baking sheet. 
Tuck about a 1/2" of the end of the swirl under each roll.
Gently press down on top of each slice, it will be a little messy, but this helps to give them their characteristic large swirl. 
If you want to add the streusel on top, do so now and crumble it onto each slice. Gently press the streusel into each slice then top the streusel on each roll with a couple of teaspoon dollops of the remaining jam. 
Leave the rolls to proof for about 20 minutes, they should look like they have grown slightly and are a little puffy.

Bake
Once proofed, bake the rolls for 10 minutes in the preheated oven. Then, swap the pans and rotate them and bake for another 10-15 minutes until golden brown. *If baking with streusel I recommend baking them a little longer.
While they bake, prep the lemon glaze.

Lemon Glaze
Scoop the powdered sugar into a medium mixing bowl and add in the lemon juice.
Whisk to combine to a thin glaze that is about the thickness of maple syrup.

Finishing
Once baked a slightly golden brown, take the baking sheets out of the oven and place on to wire cooling racks.
Immediately brush/drizzle the lemon glaze onto the rolls. Then leave them to cool for at least 5 minutes before serving.