Activate the yeast by pouring it into a small bowl with warm water. Let it dissolve completely.

In a large bowl, combine the brown sugar, softened butter, sea salt, and hot water. Stir well until everything is mixed evenly. Allow it to cool down for about 5 minutes.

Using an electric mixer on low speed, blend in 3 cups of the whole grain flour into the cooled mixture. Continue mixing for about 3 minutes on medium speed, ensuring the mixture is smooth.

Gradually add the remaining 1 1/2 cups of whole wheat flour and the activated yeast. Stir the mixture with a spoon until it forms a cohesive dough, adding 2 1/4 to 2 3/4 cups of all-purpose flour until the dough no longer sticks to the sides of the bowl.

Transfer the dough onto a floured surface and knead it for about 10 to 15 minutes, gradually incorporating the remaining 1/2 to 1 cup of all-purpose flour until the dough becomes smooth and elastic.

Grease a large bowl with vegetable shortening and place the dough inside. Loosely cover the bowl with plastic wrap and a cloth towel. Allow the dough to rise in a warm place (around 80°F to 85°F) for 30 to 45 minutes until it doubles in size.

Generously grease 2 loaf pans with vegetable shortening. Punch down the risen dough gently to release any air bubbles and divide it into two equal portions.

On a lightly floured surface, roll out each portion of the dough with a rolling pin into a rectangle measuring approximately 18×8 inches.

Starting from one of the 8-inch sides, tightly roll up the dough, sealing the edges with your thumbs after each turn. Pinch the edge of the dough to seal the roll and press each end with the side of your hand to seal them. Fold the ends of the roll under the loaf and place it seam side down into the prepared loaf pan.

Cover the pans and allow the dough to rise in a warm place for another 30 to 45 minutes until it doubles in size again.

Preheat the oven to 375°F. Once the dough has risen, uncover it and bake in the preheated oven for 30 minutes.

After 30 minutes, reduce the oven temperature to 350°F and continue baking for an additional 10 to 15 minutes until the loaves sound hollow when tapped lightly.

Remove the freshly baked loaves from the oven and immediately take them out of the pans. Place them on wire racks to cool completely for about 1 hour before slicing and serving.