Preheat oven to 325°F (160°C). Mix almond flour, ¼ cup sugar, and salt; stir in melted butter. Press into a 9-inch springform pan. Bake 10 minutes, then cool on a rack.

Beat cream cheese until smooth, about 2 minutes. Add 1 cup sugar, sour cream, and vanilla; beat until creamy. Add eggs one at a time on low, then beat in cornstarch just until blended.

Wrap pan in two layers of foil. Pour filling over crust and smooth the top. Set pan in a roasting pan, place on middle oven rack, and pour hot water in until it reaches halfway up the springform sides.

Bake 55 to 65 minutes, until edges are set and center jiggles slightly. Turn off oven, crack door open 2 inches, and cool in oven 1 hour. Remove from water bath, cool completely on a rack, then refrigerate at least 4 hours.

Run a knife around the edge and release the springform. Dip a sharp knife in hot water and wipe dry between cuts. Slice and serve with compote or powdered sugar.