Preheat the oven to 350°F. Line your muffin pan(s) with 8 paper liners. Set aside.
Using a mini food processor or coffee grinder, grind the pistachios to a fine powder. Set aside.
In a small saucepan, melt the butter over medium heat and continue cooking it until it turns light brown in color. Remove the pan from the heat and immediately add the crushed cardamom pods and vanilla bean and seeds. Let the mixture rest for 10 minutes to infuse the butter, then strain it and set it aside.
In a medium bowl, combine the ground pistachios, rice flour, poppy seeds, sugar, sea salt and frothy egg whites. Whisk vigorously to mix everything together, then add the melted butter and whisk the batter more to completely incorporate it.
Divide the batter among the 8 muffin papers and bake the financiers for about 20 minutes or until a cake tester inserted into the middle of one of them comes out clean. Let cool completely.