Start with the base for the coaster, it's made of thick felt (mine is white) and the diameter is 8,5 cm.
Then you cut out another circle with the same measurements, in the colour of the wanted fruit (orange for orange, yellow for lemon, etc. ...).
Cut out another circle (diameter: ~7cm) out of white felt (!).
Then handsew it onto the (e.g.) orange one from step 2. Right in the middle.
Now cut out triangles (mine were 2,5cm from peak to 'bottom'), seven pieces in the colour of the felt from step 2.
Sew the triangles on the base from step 2+3.
Now take the whole top and handsew it on the very base from step 1! On the white back, it should look like this now
Now put some glue between the gap of (e.g.) orange and thick white felt on the edges.