Prepare the Dough: Combine sour cream, butter, salt, and 3 tbs of the erythritol in a saucepan over medium-low. Cook, stirring, until butter melts, 5 minutes. Remove from heat and cool for about 15 minutes.

Stir together yeast, water, and remaining 1/2 tablespoon granulated erythritol in a 1-cup glass measuring cup; let stand 5 minutes.

Combine sour cream mixture, yeast mixture, egg, and 1/3 bag of Ketonia bread mix in an electric stand mixer fitted with paddle attachment. Beat at medium speed until smooth, about 1 minute. Reduce speed to low; gradually add the rest of the mix, beating until dough forms.

Turn out onto a surface and knead until smooth and elastic, about 10 minutes. (It should be tacky but release easily from the surface.) Cover; let rise in a warm place until doubled in size, 1 hour..

Meanwhile, prepare the Praline-Cream Cheese Filling: Beat cream cheese, erythritol, cinnamon, and vanilla with an electric mixer on medium speed until smooth. Beat in egg.

Prepare the baked cakes: Gently punch dough down. Spread the filling over the rectangle, leaving a 1-inch border. Sprinkle with 1⁄2 cup of the pecans. Starting at 1 long side, carefully roll up the rectangle in a jelly-roll fashion. Place, seam side down, on a large parchment paper-lined baking sheet. Bring ends of roll together to form a ring. Moisten ends with water; pinch together to seal. Cover; let rise in a warm place until doubled in bulk, 1 hour.

Preheat oven to 350°F. Uncover dough ring, and bake in preheated oven until deep golden brown and done, about 25 minutes. Cool cake completely on pan set on wire racks, about 1 1⁄2 hours.

Prepare the Creamy Vanilla Glaze: Stir together powdered erythritol, melted butter, and vanilla. Stir in 1 1/2 tablespoons of heavy cream. Add additional cream, 1 teaspoon at a time, until pourable but still opaque. Pour evenly over cakes; sprinkle with sparkling erythritol, alternating colors to form bands.