orgeat syrup

500 gr blanched whole almonds
800 ml water
700 gr table sugar
100 ml vodka or brandy
2 tbsp orange or rose flower water

Place the almonds in a bowl and cover with cold water and allowed them to soak for 30 minutes. Drain and discard this water, then crush the almonds using a rolling pin, or you could use a food processor to chop them to a fine grind. If you need to, you can add some of the water to the food processor. Transfer the crushed almonds to a large bowl and mix them with the water, let stand for one to two hours. Place a damp cloth or cheese cloth in a mesh filter, over another bowl, and strain the almond and water mixture squeeze the cloth to extract all the liquid.

Put the chopped almonds back into the almond water, let it stand for another hour and then strain again. Repeat a third time if you wish. This is will get all the oils out of the almonds.

Note: To speed up the process you can gently heat the almond water to 50°C (125°F). If you do this, you can cut the soak times to about 15 minutes.

Pour the strained liquid into a pan, discard the almond pulp, add the sugar and cook over gentle heat, stirring constantly. Remove from the heat when the sugar is completely dissolved. Allow to cool for 15 minutes and then add the brandy or vodka and the orange flower water. Store the orgeat in a clean glass bottle.

Once the orgeat has cooled down it is ready to use.

from artofdrink.com (though it's cited elsewhere)

when i have time, i'll boil the ingredients down to "normal" measurements, and simplify the explanation.