In a large shallow bowl or pie plate, crack the eggs and whisk them together. Add pumpkin puree (measure exactly ¼ cup), whole milk, heavy cream, and granulated sugar. Whisk in vanilla extract, cinnamon, pumpkin pie spice, and salt. Mix until completely smooth with no pumpkin lumps. Let sit for 1 minute to allow spices to bloom.

If using a whole loaf, cut bread into thick slices about ¾ inch. Dip each bread slice into the pumpkin custard mixture. Let soak for 20-30 seconds per side. The bread should be saturated but still holding together, not falling apart.

Heat butter in a large skillet or griddle over medium heat. Wait until butter is melted and foaming but hasn't started browning yet. Place soaked bread slices in the buttered pan.

Cook for 3-4 minutes without moving them. Flip when edges are golden and top looks set. Cook another 3-4 minutes on the second side until deep golden brown. Add fresh butter between batches. Keep finished pieces warm in a 200°F oven while cooking the rest.

Transfer cooked french toast to plates immediately. Top with a pat of butter so it melts down. Pour warm maple syrup generously over the top. Add whipped cream if desired. Dust with powdered sugar for prettier presentation. Serve immediately while hot.