Initially I tried to make this as two separate pieces, the cross and then the circle. I quickly realized I have no idea how to make those circular cuts in the cross it’s self.
I would do the cross itself as one piece and the circle behind it as another. To get the circle cuts in the corner, you’ll need a little more geometry to shape it. You’ll need at least two more edges on either side of the corner for the shape and if you’re using a subsurf modifier, you’ll need an extra one or two around the corners of the circle.
Here’s a screenshot to show what I mean. The highlighted edge loops are the ones controlling the shape. The others are helping to sharpen the edges. I used a mirror modifier so only half had to be modeled.