1. Preheat the oven to 350°F, grease and flour a 9 x 13-inch pan.
2. For the cake: Cream the butter and sugar together until light and fluffy, scraping the sides and bottom of the bowl at least once. Add the eggs, one at a time, mixing well between additions. Add the extracts and mix to combine.
3. Whisk the cake flour, baking powder and salt together, and add to the butter mixture
4. alternately with the milk.
5. Pour the batter into the pan, spread it out, and bake for 25 to 30 minutes, until the top is springy to the touch and a pick inserted in the center comes out clean. Remove from the oven and cool on a rack for 10 minutes.
6. After 10 minutes, loosen the sides of the cake from the pan. Place a piece of parchment ant a cooling rack on top of the pan, and turn everything upside to finish cooling completely.
7. For the frosting: Put the butterscotch chips and half of the butter in a heatproof bowl, and melt together over low heat or at low power in the microwave. Stir until smooth; if it looks a little broken, that's ok.
8. Put the other half of the butter in a mixing bowl with half of the confectioners'sugar. Mix until smooth, then add the melted chip mixture. Add the rest of the sugar and beat again until you have a smooth frosting. Add the milk if necessary to make the frosting a spreadable consistency.
9. To assemble: Spread the frosting evenly over the inverted cake. To invoke the traditional Krimpet waviness, use a cake comb to put waves in the frosting.
10. Cut the cake in thirds lengthwise, then in nine rows of one and a half-inch strips to make 27 pieces.