Melt the chocolate. All 300 g, chopped, in a heatproof bowl. Over a double boiler, with the bowl set over a pot of hot water without touching the water, or in the microwave in 20-30 second bursts, stirring in between.
Add the butter and almond butter. When the chocolate is almost melted, the 40 g of cubed butter and the 60 g of almond butter.
Stir until smooth. It should be a thick, very glossy cream with no lumps.
Add the puffed rice. All 70 g at once.
Fold gently. With the spatula, folding until all the rice is coated in chocolate.
Line the pan. With parchment paper hanging over the sides: you'll use it to lift the turrón out.
Pour into the pan and smooth. Spread the mixture out and smooth the top without pressing down: if you squash it, it loses its crunch.
Chill it. At least 2 hours, ideally 8 or overnight. The longer it rests, the cleaner it cuts.
Lift it out. Pulling up on the parchment paper by the sides.
Cut into pieces. With a large knife, pressing straight down. It makes 16 pieces of about 30 g (1 oz).