The day before you plan on baking your buns, prep the dough and date caramel. Soak the pitted dates in warm water for 10 minutes, then drain and transfer to a food processor with the rest of the date caramel ingredients. Process until caramel is smooth and transfer to a resealable container to store in the refrigerator overnight.
Next, prep the dough. Add the flour and yeast to the bowl of a stand mixer fitted with the dough hook attachment. Mix on low for 15 seconds.
Add eggs, milk and salt and mix on medium-low for 4 minutes, scraping down the sides as needed. Add the ½ cup plus 2 tablespoons butter, a little at a time, beating until incorporated after each addition. Stop the mixer, scrape down the sides and mix on low for another 5 minutes.
Turn dough out onto a lightly floured surface and knead for a few minutes, adding a small sprinkle of flour if the dough gets too sticky to handle. Transfer dough to a bowl coated with cooking spray, cover with plastic wrap and let rise for one hour.
After the first rise is complete, turn the dough out onto a lightly floured surface once again and knead gently for just a few minutes. Return dough to the bowl, cover once again and let rise in the refrigerator overnight.
The next morning, remove the dough from the refrigerator, turn it out onto a lightly floured surface once again, and roll dough out into a 16-inch square. Also remove the date caramel from the refrigerator at this time to let it come to room temperature.
Spread 2-4 tablespoons melted butter onto dough with a pastry brush.
In a small bowl, mix together the cinnamon and sugar and then sprinkle this mixture over the melted butter on the dough. Let sit for a moment while you prep the oven and baking pan.
Preheat the oven to 350 degrees Fahrenheit. Spray a jumbo muffin tin or popover pan generously with nonstick cooking spray. Place 2 tablespoons of the date caramel in each cup followed by 2 tablespoons of the toasted hazelnuts.
Now, return to your dough and sprinkle the remaining hazelnuts over the cinnamon sugar mixture. Roll the dough up into a cylinder and trim off the ends, pinching it together at the seams. Cut the cylinder into 6 equal pieces and place each piece in one of the muffin tins, on top of the date caramel and hazelnuts. Press your finger into the middle of each one to spread it to the edges.
Place sticky buns in the 350 degree oven and back for 20-25 minutes, or until slightly golden. Immediately invert onto a Silpat. If any of the caramel stays stuck in the pan, simply scoop it out with a spoon and on top of the now inverted buns. Let cool completely (or almost completely) before serving.