In a medium bowl, toss together the flour, baking soda, baking powder and salt.
In a stand mixer, cream the butter and white sugar at medium speed until light and fluffy, about 3 minutes.
Add the eggs, one at a time, beating until each is incorporated.
Add the vanilla and sour cream and beat at low speed until combined.
Add the dry ingredients and mix on low speed until just combined.
Divide dough into two sections. Flatten into rectangles about 1 1/2 inches thick (this will make rolling it out easier), then wrap with plastic wrap. Chill in the refrigerator overnight or at least two hours until firm.
Preheat the oven to 425F. Line large baking sheets with parchment paper.
Flour the counter, the top of the dough, and your hands. With a rolling pin, roll the dough out to 1/4-inch thickness.
Using a 2.5 round cookie cutter, cut out circles and transfer to a baking sheet.
Alternately, you can use floured hands to shape cookies into 2.5 inch discs roughly 1/4-inch thick.
Bake for 7 minutes, until pale golden. Allow to cool completely on wire rack before dipping.
For chocolate, melt semi-sweet chips and shortening on a double boiler on low heat, or in the microwave in 30-40 second intervals at 50% power.
Dip cooled cookies halfway into the chocolate, place on wax paper and immediately sprinkle with toffee bits.