Choose a knit fabric with some stretch
Measure the head circumference and desired beanie height
Draft a simple beanie pattern with a folded brim or without one
Cut two mirrored fabric pieces
Place the fabric pieces right sides together
Pin or clip the curved edges
Sew along the curved sides with a stretch stitch or zigzag stitch
Leave the bottom open
Repeat for the lining if using one
Turn one layer right side out and place it inside the other layer
Align the seams and edges
Sew around the bottom edge, leaving a small opening if needed
Turn the beanie right side out through the opening
Close the opening by hand or machine
Fold up the brim if desired
Press the seams lightly if appropriate for the fabric