Preheat oven to 350°F(175°C) and line a baking sheet with baking paper.
Cream the butter and sugar together in a mixing bowl. You can use a wooden spoon or electric mixer. Add the syrup, mixing well.
Add in the flour, baking soda, and vanilla (vanilla sugar or extract). Mix until the dough starts to come together but isn't fully combined.
Grate (or finely chop) the almond paste and add to the dough. Mix the dough together with a spoon our your hands until it forms a large ball.
Divide the dough in half and roll each half into a long sausage. Set the two sausages on your baking sheet, spaced well apart, and lightly press down with your fingers.
If you want, you can whisk an egg and brush it on the cookie dough.
Sprinkle the dough with almond slices. Bake for about 15 minutes, until the cookies are a nice golden brown color.
Let the cookies cool for a couple of minutes and then slice them diagonally into about 24 bars.