3/4 cup fresh masa or 2/3 cup masa harina
5 Tbsp. unsalted butter, plus more
1¼ cups buttermilk
¾ cup gluten-free cup-for-cup flour (such as King Arthur Measure-for-Measure Flour)
2 Tbsp. fine grind cornmeal
½ tsp. baking powder
½ tsp. baking soda
½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt
2 large eggs
2 Tbsp. sugar
If using masa harina, combine in a medium bowl with ½ cup hot water and, using a rubber bowl scraper, stir and mash together until no dry spots remain. Cover with a plate or plastic wrap and let cool, about 30 minutes.
If using fresh masa, crumble into a medium bowl.
Melt 5 Tbsp. butter in a small saucepan over medium heat. Pour in buttermilk and remove from heat. Set aside.
Whisk flour, cornmeal, baking powder, baking soda, and salt in a large bowl to combine.
Add eggs and sugar to masa and whisk until only a few lumps remain. Add half of buttermilk mixture and whisk until homogeneous. Add remaining buttermilk and whisk again to combine. Add to bowl with dry ingredients and mix until no dry streaks remain.
Heat a large griddle or 2 cast-iron or nonstick skillets over medium; brush with butter. Working in batches, scoop ¼-cupfuls of batter onto griddle and cook until bubbles form on the surface and undersides are golden brown, about 3 minutes. If undersides are browning too quickly, reduce heat to low. Flip pancakes and cook until golden brown on the other sides, about 2 minutes. Transfer pancakes to individual plates or a platter. Serve with butter and maple syrup.