Shares of Shake Shack (SHAK 3.45%) were surging last month as the fast-casual burger flipper delivered a strong earnings report and impressed Wall Street with its guidance, which called for improving margins in 2024.The company is also accelerating its restaurant growth, tapping into demand for a brand that has always been one of the highest-trafficked fast food chains.According to data from S&P Global Market Intelligence, Shake Shack gained 40.7% last month. As you can see from the chart below, the earning ...