Mix flour, 1 tablespoon of sugar, salt and egg. Gradually stir in milk and mineral water. Let dough rest for about 15 minutes. Wash the orange, grate dry and tear off the peel as zests.
Then peel the orange so that the white skin is completely removed. Cut the orange into slices. Brush a pan with a little oil. Put 1/4 of the batter into the pan and spread it thinly on the bottom of the pan by tossing it back and forth.
Bake from both sides until golden brown. Bake another 3 crêpes from the remaining dough. Melt 3 tablespoons of sugar in a pan until golden brown. Add butter and deglaze with orange juice. Steam orange slices on both sides for about 1 minute.
Take out, zest and stir liqueur into the sauce. Pull crêpes through the sauce one after the other, fold into quarters. Arrange crêpes with orange slices on plates. Sprinkle with pistachios.