Butter a 7x11-inch pan (or 9x13 for slightly thinner roca). Sprinkle 1 cup of toasted almonds on bottom of the pan.
In a heavy saucepan at medium-high heat melt butter and add brown sugar. Stir until gently boiling. Reduce heat to medium or medium-low and boil 12 minutes exactly, stirring constantly. If you use an instant read thermometer, make sure it's about the right temperature. Pull it off the heat when it has reached the hard-crack stage (300°F)- or when the mixture starts to separate (the oil starts to separate from the sugar). If it gets higher than 320°, it will not remain solid.
Remove the mixture from heat, give it a good stir to mix up that butter and sugar one more time, and immediately pour the hot mixture into the pan over the almonds.
Place the chocolate bars on top. Let them sit a minute or so until melted, then spread chocolate around carefully. Sprinkle with the remaining toasted almonds, and gently press them into the chocolate.
Cool completely, and then break apart into chunks with a sharp knife. Store in a covered container.