In mixing bowl, beat butter, sugar, salt, baking powder and vanilla until light and fluffy.

Add the egg and beat well.

Add the sour cream, cornstarch and half of the flour. Mix on low until incorporated. Add the remaining flour and mix just until blended.

Divide dough into 2 parts. Form a disc for each. Wrap in plastic wrap and refrigerate at least 1 hour.

Preheat oven to 350 degrees.

Roll one disc into a rectangle about 1/4 inch thick. Use a pastry wheel to cut into rectangular sticks. Place on a lined baking sheet. Repeat with other piece of dough.

Bake 10-12 minutes. Remove from sheet to cool.

Pour white chocolate discs into a bowl. Melt white chocolate discs in the microwave. Dip edge of cookie into the melted chocolate and dip into assorted sprinkles.

Place on a drying rack to set.

Store in an air-tight container or freeze up to 3 months.