Did Joseph recognize his brothers when they came before him in Egypt?
Yes. Joseph knew his brothers as soon as the ten men came before him in Egypt; he immediately recognized who they were. They, however, did not know or recognize Joseph. The account presents this contrast as a picture of Christ's first coming, when the Lord knew Israel, but they did not recognize Him.
Les teaches that in Genesis 42 Joseph's ten brothers went down to buy grain in Egypt. When they came before Joseph, he immediately knew who they were as soon as they stepped into his environ, but they did not know him. Les connects this to Christ at His first coming: the Lord knew Israel from their beginning and presented Himself in clear language, yet they did not recognize Him. This is the lesson Stephen drives home, using Joseph's circumstances as an analogy. Later, in chapter 45, they return a second time to refill their sacks.