In a small bowl, combine the 10-grain cereal mix and boiling hot water. Let it sit and hydrate for about 15 minutes. During this time, the grains will soak up all of the water and cool slightly. Allow it to cool to around 100°F before mixing the recipe.
In the bowl of a stand mixer and on low speed, combine the hydrated and cooled 10-grain cereal, room temperature buttermilk, instant yeast, salt, melted butter, honey and eggs. Mix them with the paddle attachment until they are fully incorporated.
Add the bread flour and whole wheat flour. Using the dough hook attachment combine until it's fully mixed together and a soft dough forms. Stop the mixer and let is rest for about 10 minutes. Cover with plastic wrap or a kitchen towel to keep it from drying out. This rest time allows the dry ingredients to get fully absorbed before kneading.
Knead the dough on low speed for 5 minutes. If the dough is not cleaning the sides of the bowl after about two minutes of kneading, stop the mixer and lightly tap on the dough with your finger. It should feel soft and pliable but not be excessively sticky or wet. Add 1-2 Tablespoons of flour if needed and mix on low speed until fully incorporated. Stop the mixer and check the dough with your fingers again. As soon as it feels right, continue kneading on low speed. *You really want to avoid adding too much flour to your dough - it will cause your rolls to be dry and dense.
After kneading, put the dough in a large bowl greased with olive oil or nonstick spray. Turn the dough to coat all surfaces with oil. Cover the bowl with a kitchen towel or plastic wrap, put it in a warm place in your kitchen and let it rise until doubled in size. Depending on how warm your kitchen is, it will take around 60-90 minutes.
Remove dough from bowl. Divide the dough into 12-24 equal pieces (depending on how big you want your rolls). Round out the dough balls - be sure to watch my roll shaping video for my easy technique to make perfectly round, beautiful bread buns!
Place them in a greased 9x13 baking pan (I use either a ceramic baking dish or metal deep dish baking pan - like a cake pan). Space them close, so that they are just barely touching each other - this will force them to rise and bake nice and tall!
Cover with plastic wrap or a kitchen towel and let rise until doubled in size, about 45-60 minutes.
Preheat the oven to 375°F.
Brush the rolls with melted butter and, if desired, sprinkle on some sea salt flakes!
Bake for 18-22 minutes, until they're golden brown. Brush with more melted butter when they are hot out of the oven!
Pull apart and enjoy!