In the bowl of a stand mixer fitted with the paddle attachment, beat together the mascarpone, milk, and egg at medium speed until smooth, pausing to scrape down the sides of the bowl with a spatula as needed. Add the honey, melted butter, grapefruit juice, grapefruit zest, and vanilla extract and mix until smooth.
In a separate bowl, mix together the flour, baking powder, baking soda, and cardamom. With the mixer going at low speed, mix the dry mixture into the wet mixture until *just* combined to form the batter. Do not over mix.
Heat 1 tablespoon of the solid butter in a medium frying pan over medium heat. Add just enough batter to create a small 3-inch pancake, fitting a few in the pan if you can (just make sure they don't touch each other). Cook until golden on both sides, adding another tablespoon of butter to the pan between every few pancakes if needed.
Whisk together the creme fraiche and maple syrup until smooth.
Arrange the grapefruit slices on two plates. Place 5 pancakes on each plate and drizzle them pancakes with the maple creme fraiche. Top with the kumquat slices, pistachios, maple syrup, and serve.