Rows and rounds.....

This square is started off by working in rows to create the initial grid and is then worked rounds until it is the right size:

The initial grid is created by working 17 chains, in the 8th chain from the hook work a treble crochet, *chain 1, skip 2 chains, work 1 treble, repeat from * to end. 4 chains, *treble in treble from previous row, chain 1, repeat from * to end. Repeat previous row twice more to give a 4x4 grid.
5 chains in a corner space, 3 trebles. Work 3 trebles in each space from previous round - in the corners work 3 trebles, 2 chains, 3 trebles. In the final corner work 2 trebles and join to the initial 5 chains.
5 chains in a corner space, 2 trebles. Work 2 trebles and 2 chains in each space from previous round - in the corners work 2 trebles, 2 chains, 2 trebles. In the final corner work 1 treble and join to the initial 5 chains.
5 chains in a corner space, 2 trebles. Work a treble in each treble from the previous round and 2 trebles in each space from previous round - in the corners work 2 trebles, 2 chains, 2 trebles. In the final corner work 1 treble and join to the initial 5 chains.
Work two rounds of double crochets to finish off.
I chose to change colour at the end of each round but this is optional.