Combine butter, water, yeast and sugar. Mix gently and let sit 3-5 minutes until bubbly.
Add eggs, salt, baking powder and 2 cups flour. Mix well. Add remaining 4 1/2 cups flour and mix until combined.
Cover bowl with plastic wrap sprayed with nonstick spray and let rise about 1 hour, or until doubled in size.
Divide dough in half and roll one half into a long rectangle (about 20" x 10").
Combine 1/2 cup brown sugar and 1 tsp cinnamon in a bowl.
Spread 4 Tbs of softened butter over the rectangle of dough. Sprinkle with the brown sugar mixture.
Roll the dough up longwise to form a log.
Using flavorless/cinnamon floss or fishing line or string, slide the floss under the log to the middle. Pull up both ends of the floss until they cross each other, cutting the log in half. Cut each of those halfs in half. Then cut each section into thirds, making 12 pieces.
Place rolls in a greased 9x13" baking dish. Roll out your other half of the dough and repeat the process to make another pan of cinnamon rolls. Cover and let rise 30 minutes.
Bake at 400 degrees for about 12 minutes, until golden brown on top.
Add all frosting ingredients into a bowl. Beat together until smooth and creamy.
Frost cinnamon rolls after they've cooled for about 10 minutes.