Warm, pillowy beignets with a delicate tang from active sourdough are fried to a golden crisp and lavishly dusted with powdered sugar. Light yet indulgent, they melt in the mouth with a tender crumb and subtle richness of cream and butter.
Warm the cream in a small saucepan until warm but not hot; whisk in the sugar to dissolve, then let cool slightly.
Transfer the cream mixture to a large bowl and add the active sourdough starter, egg, melted butter, flour, and salt; mix until a shaggy dough forms.
Knead on a clean surface for about 5 minutes, until the dough feels smooth.
Place the dough in a lightly greased bowl, cover with a tea towel, and let rise in a warm place until doubled, about 6–8 hours (longer if your kitchen is cool).
Turn the dough onto a lightly floured surface; roll into a large rectangle about 1/4–1/2 inch thick.
Cut into 1 1/2-inch squares using a sharp knife or pizza cutter.
Arrange the pieces on a parchment-lined baking sheet, cover with a tea towel, and let rise 1 1/2 to 2 hours, or until about doubled.
Heat 2–3 inches of neutral oil in a deep, heavy pot to 330–350°F (165–175°C).
Fry 3–5 beignets at a time for 1–2 minutes per side, until golden brown.
Remove to a cooling rack or paper towel–lined tray to drain excess oil.
Dust generously with powdered sugar while warm; repeat with remaining dough and serve.