Melt the butter in a medium saucepan over medium heat. Continue to cook the butter until it turns a light amber color and smells nutty and toasted, about 5 to 10 minutes. Remove from heat and scrape the paste in the vanilla bean pod into the butter. Toss the vanilla bean husk in there as well and let it sit for 20 minutes to infuse the flavor throughout the butter. Remove and discard the husks.
Preheat the oven to 450 degrees Fahrenheit. Mix together the powdered sugar, almond meal, cake flour, cinnamon, and salt in a large bowl. Add the egg whites and whisk until combined. Add the vanilla butter mixture and stir until combined.
Pour the mixture into a well-greased muffin pan, filling the wells about 3/4 full. Bake at 450 for 7 minutes, then quicky remove the pan and place a thin pluot slice on top of each financier. Place the pan back in the oven, lower heat to 400, and bake another 7 minutes. Turn the oven off and let them rest for an additional 7 minutes inside the oven before removing them and allowing them to cool to room temperature.
Sprinkle with a teaspoon or two of powdered sugar and serve.