Divide the potatoes into 1-centimeter-high slices, then with a cookie cutter cut out many small stars.
Also cut the salmon into stars, which you will overlap with some chips.
Mix the butter with the mascarpone and lemon.
Use this cream on potatoes as a base for caviar, to be placed either on top of salmon or on plain stars.
Notes
For an even more original touch, you can add a pinch of chopped chives on top of the caviar for a contrast of colors and flavors. If you want a lighter version, replace the mascarpone with Greek yogurt.