OK, here goes......... hope it makes sense.
I use inkscape for this. it might be possible in scal but I've not done it (I design in inkscape and use scale to cut)
you need two shapes, your card base (CB) and your lace topper (LT)
the card base can be a rectangle or square with a centre line (fold) or two welded rounded rectangles or squares - I shall just refer to this as card base or CB
the lace topper is the design that you will cut from the card base. I shall call this (surprise!!) lace topper or LT
place the LT on your CB where you want it so it goes across the fold line a little.
now what we want is the part of the LT that is above the score line (on the back) of the CB needs to be cut but the problem is, the bottom part (on the card front) needs to be cut but in a different way. the top part is an outline the bottom part we need the "holes" cut out.
so first off, we need to split the LT into two bits. the top bit (above the fold) and the bottom bit (below the fold) I find the easiest way is to draw a straight line across the LT where I need/want to split and select both the line & LT and then go
Path>Cut Path
now you have a top bit (above the score line) and bottom bit (below the score line)
if you find your LT disappeared, look at the screen and you should see the topper is outlined in lots of dashed lines - just select a stroke colour and it should appear - if it still does not try raising it (or lowering the CB) as it may be it's below the card
SAVE YOU WORK!!!!! (if anything goes wrong, you can at least come back to this part and start over again)
so now, carefully as you don't want to move anything click the bottom part outside edge and hit delete. keep an eye on what does disappear as it's easy to select something you want. if you get it wrong, undo is your friend
now, select a "hole" and your CB and then go
path>exclusion
this will remove the "hole" from the card
repeat this with each "hole" select it and the CB and go path>exclusion
once done, select everything and go
object>group
this is make sure that the outer top part that you want cut is not moved by accident
That should give you the card base you require. when you fold along the fold line the bit cut from the back of the card should pop up and make the card as in the pic (but with your choice of topper of course)
hope this helps.
Gaz