I've done it like you would do a "snowball corner." So, cut your stem square 3 1/2." Then cut two background pieces about 3" square (2 3/4" would give you a wider stem). Draw a diagonal line from one corner to the other on the back of each background square. Place the background squares on opposite corners, and sew on the lines. Press away from the stem on the front, and trim off the seam allowances. There's a little waste, but it turns out pretty perfect.