Adjust oven rack to middle position and heat oven to 450°F. Line a sheet pan with parchment paper or spray a sheet pan with cooking spray.
Measure 1 cup of buttermilk and place in the freezer for 10 minutes while prepping other ingredients.
Place butter in a microwave-safe bowl, cover and heat on high for 30 seconds. If not completely melted, return to microwave for 10-second intervals until melted. Set aside to cool a little while prepping other ingredients.
Whisk flour, baking powder, baking soda, sugar,and salt in large bowl.
After buttermilk has been chilled in the freezer for 10 minutes, combine it with 8 tbsp of the melted butter. (Reserve the last tbsp for brushing on the baked biscuits.) Stir with fork until small clumps
Add buttermilk mixture to dry ingredients and stir with a rubber spatula just until all flour is incorporated and batter pulls away from sides of bowl. The dough should be stiff and not super wet. If the dough is wet, add more flour 1 tbsp at a time, stirring to combine, until fairly stiff.
Generously flour a work surface. Dump biscuit dough from bowl onto prepared work surface and turn to coat with flour. Knead on counter 5-6 times (about 30 seconds). Flip dough over on the work surface again to coat with flour then pat into a 6-inch square. It should be a 1½-2-inches in height.
Cut four biscuits with a 2 1/2-inch biscuit cutter. Place biscuits on the prepared sheet pan. Knead scraps a few times till they hold together, then pat into a small rectangle and cut two more biscuits. Transfer last two biscuits to the sheet pan, spacing about 1 1/2 inches apart.
Place in oven and bake until tops are golden brown and crisp, 8 to 18 minutes. (start checking them after 8 minutes as ovens vary. You want them to be a nice golden brown, but not too brown).
In a saucepan saute onions in oil until translucent. Add other ingredients and simmer until thick like a jam. Cool before serving.
Top biscuits with marmalade and an extra slice of Red Butte.