how do i cut this piece

[cwsmith]

How many of these do you have to make, and which way do you want the grain to run.

If it doesn't matter (grain) then I'd simply cut a board to the desired width, then run it across the router table a few times to route out that bottom width.

Then I'd simply cut off whatever number of piece that I'd need.

At that point you'd have the number of pieces cut to width and length, with the bottom area routed out per your illustration.

All that would be left would be to cut the rabbets along the top edge. For that, I'd hold them in a parallel clamp and pass them over the router table.

If you need the grain running specifically, then I'd simply adapt my original boards to do so.

CWS

[LCHIEN]

Did it.
Most of your ideas involved making the dado first. But i had stated I had already cut the pieces except for the dado.
So Just lined up all the pieces and clamped them together, carefully aligning the edges and the bottoms. That gave me a long enough edge I could run it against a fence and make all the dadoes simultaneously.
I had to make many passes since the dado was 2 inches wide.

I flipped it every pass so I had to make only half the adjustments and the dado was exactly centered.

[woodturner]

Did it.

<chest bump>