Fry the onion in the olive oil until soft but not browned. Add garlic and continue frying another 30 seconds. Add the wine and cook until wine is almost absorbed/evaporated. Remove from heat.
Make the filling by whisking the egg, then mixing in the cream. Add the crab, cheese, parsley, and onions. Mix. Set aside.
Make the dough by mixing the flour and salt in a large bowl. Cut the butter into small cubes. Use fingers to squeeze the butter into the flour by grabbing chunks of flour and butter and squeezing to combine. Continue until it looks like a bunch of small bread crumbs.
Add water a little at a time, continuing to squeeze as before, until the flour and water form a stiff dough.
Dust a counter with flour and roll the dough into a thin sheet. Use a 2 1/2 inch cookie cutter to cut circles of dough. Place these into a muffin tin to form the crust of the tartlets. When you run out of dough to cut, collect the scraps, re-roll them and cut more circles. You should get close to 24.
Pour the filling evenly into each tartlet. Bake at 375 for 25-30 minutes. They should be set and golden-brown in color.