Melt the butter in the saucepan on high or med-high, stirring constantly. As the butter is about ½ melted, stir in the sugar. Continue stirring. As the sugar and butter bind together, add the chopped almonds. Keep stirring constantly to prevent the butter from separating from the mixture. Continue until the toffee mixture reaches hard crack on the candy thermometer (about 300+ degrees). The candy should be a mapley brown color and all bound together.
Remove from stove and stir in the teaspoon of vanilla. Let rest for 30 seconds to a minute. Then divide the mixture, pouring it between the two cookie sheets, and spread the toffee as thinly as possible with spatulas. Two people are helpful here, but you can manage alone.
Melt the chocolate in a microwave or double boiler. Spread the chocolate thinly over the toffee and sprinkle with the ground almonds. Let cool until the chocolate solidifies.
Turn the toffee over, and at this point, the sheet of toffee may break into smaller pieces. Nevertheless, repeat the chocolate and ground almond step on this second side. Let cool.
Break into pieces and enjoy. No need to refrigerate. Store at room temperature in metal tins or plastic containers.