How to Make It
Preheat oven to 340°F. Very lightly butter an 8-inch-square baking dish. Set aside.
Melt butter and chocolate in a large, heavy saucepan over low. Cook, swirling pan occasionally, until mixture forms a sludgy paste in buttery liquid, about 10 minutes. (The chocolate will not completely dissolve in the butter.) Remove from the heat. Add brown sugar and ginger; stir until mixture is glossy and fudgy. Let cool 10 minutes. (Don’t worry if mixture separates as it stands.)
Add eggs; whisk gently until completely incorporated. Add almond flour and chopped walnuts; stir gently to combine.
Pour batter into prepared baking dish, and bake in preheated oven until top is dark brown and crisp around edges, about 50 minutes.
Cool in pan on a wire rack 30 to 40 minutes before cutting and serving with crème fraîche and raspberries.