How to Make It
Gently stir together crabmeat, mascarpone, shallot, chives, and 1/4 teaspoon salt in a bowl until combined. Chill until ready to use.
Whisk together flour, cornstarch, baking powder, and remaining 1/2 teaspoon salt in a large bowl. Gradually whisk in beer until just blended (batter will be thick).
Pour oil to a depth of at least 3 inches into a Dutch oven or large saucepan. Heat over medium-high to 375°F. Line a plate with paper towels.
Roll 1 heaping tablespoon crab mixture into a loose ball; drop into batter in bowl. Spoon batter over ball to coat evenly. Lift ball from batter using spoon, trying to collect as much batter on spoon with ball as possible. Gently slide the beignet into hot oil from just above the surface. Repeat process with about 2 or 3 additional beignets, making sure not to overcrowd Dutch oven. Fry, turning occasionally, until crisp and deep golden brown, about 3 minutes. Using a slotted spoon, transfer beignets to paper towel–lined plate; season with salt. Repeat process with remaining crab mixture and batter, letting oil return to 375°F between batches. Serve hot.