In a medium sized bowl, mix together 1/2 cup packed brown sugar, 1 tsp cornstarch, 1 tsp ground cinnamon and 1/4 tsp salt and set aside. Cover and set aside.

In a large bowl or the bowl of a stand mixer, combine 4 1/4 cups of flour, 2 packets of instant dry yeast and 1 tsp salt.

In a separate bowl, combine 1 cup milk, 1/2 cup softened butter and 1/2 cup granulated sugar. Heat for 1 minute in the microwave and stir to combine the ingredients. The butter should be melted.

Slowly pour the warm milk mixture into the flour mixture and mix on medium speed with a dough hook or by hand. Scrape around the edges with a rubber spatula to make sure all the flour gets incorporated.

Add in 2 large eggs, one at a time. Mix on a medium speed until a sticky dough ball forms.

Continue to mix the dough on a medium-low speed for 2-3 minutes until the dough becomes more elastic.

Keep mixing the dough and add additional flour 1 Tbsp at a time until the dough is tacky but no longer sticky (usually takes me 3-4 additional Tbsp of flour). It should pull away / / no longer stick to the side of your mixing bowl once it's ready to rest.

Cover your bowl with plastic wrap and set aside. Let the dough to rest for 10-20 minutes to allow the gluten to relax. This will make it easier to roll out.

Place the dough on a lightly floured surface and roll it into a large rectangle that's about 14 in x 18 in. The dough should be about 1/2 cm thick. 

Spread 1/2 cup of softened butter evenly across the dough, leaving 1/2 inch of dough on the long side of the rectangle uncovered. This will help you seal off the roll and keep it tight).

Spread 1 cup of blueberry jam on top of the buttered section, then sprinkle the brown sugar filling over the buttered/jam section.

Roll the dough horizontally toward the uncovered strip.

Cut 12 equal pieces and place in a greased 9 in x 13 in pan using dental floss. It sounds weird but it gives you super clean cuts!

If you are making these cinnamon rolls the night before, cover the cinnamon rolls with plastic wrap and place in the fridge overnight.

If you make these the morning of, at this stage you can let them proof in a warm place for about 30 minutes. I like to preheat my oven to 200 F, turn it off, then place my cinnamon rolls into the oven to proof because my apartment is always cold.

If you make these cinnamon rolls the night before, take them out of the fridge 1-2 hours before you want to bake them. Place the rolls in a warm place to thaw and proof.

Once they have risen, preheat your oven to 350 F / 175 C. Bake for 26-30 minutes, or until rolls are golden brown. Rotate the pan halfway through to help them bake evenly.

To make the glaze, stir together 1/2 cup of butter, 2 tsp vanilla extract and 1/4 tsp salt and mix with a spoon or electric mixer until combined.

Add in 1 /2 cups of powdered sugar and 2-3 Tbsp of whole milk. Stir until the glaze is smooth.

Let the blueberry cinnamon rolls cool for 10-20 minutes, then spoon the glaze over the cinnamon rolls.

Pour half the glaze over the cinnamon rolls, then mix 3 Tbsp of blueberry jam into the remaining glaze to give it a beautiful purple color. Drizzle the remaining glaze over the cinnamon rolls.

Garnish with fresh blueberries and enjoy warm!