In a big bowl mix the butter and sour cream together for 2 minutes, until smooth and creamy.
Add salt,baking soda and half of the flour to the butter mixture and mix with a spatula until it’s well mixed.
Add the second half of the flour and gather the dough into a ball.
Return the Rugelach dough into a bowl and cover with the plastic wrap, then chill for 30-40 minutes.
Meanwhile, make the filling. Mix the jam and the cornstarch and set aside.
Divide the chilled dough into halves or fourths. Roll each part into a rough 10-11″ circle (it should be just under 1/8″ thick).
Grease each circle evenly with the jam mixture, then using a pizza cutter or sharp knife,slice the dough into 12 wedges, just like you would cut a pizza or pie.
Roll each wedge up, beginning with the wide end and ending with the narrow end.
Place therolls about an inch apart on parchment lined baking sheets and bake for 20-25 minutes, until lightly golden.
Cool the Rugelach completely then dust with the sugar powder.