Grease an 8 x 8 inch pan and layer it with a parchment paper or aluminum foil in such a way so that you can lift it after setting the chocolate bars. Grease this too. Keep it aside.
To make the bottom layer, crush the marie biscuits to a fairly fine powder form. (You can either put them in a ziplock bag, seal the bag and crush using a rolling pin or for a quicker method, if you have a food processor, you can use this too.)
Add the melted butter and crunchy peanut butter and mix well till it's completely combined.
Spread this in the greased and lined pan, press it well with the back of the spoon to set it well and make a smooth surface.
To make the chocolate-peanut butter layer, chop the chocolate to fairly small pieces. Place it in a bowl, you need to melt this.
In a double boiler (place the bowl with chocolate over a pan of simmering water) or melt the chocolate in a microwave.
Over the double boiler, keep stirring the chocolate. Once it starts to melt, add about 2 tablespoons of peanut butter. Keep stirring till the chocolate has completely melted and the peanut butter is well incorporated into the chocolate.
Simultaneously, in a small saucepan, melt the remaining 2 tablespoon of peanut butter on a low heat till it is fairly smooth.
Pour the molten chocolate-peanut butter mixture over the biscuit crust and spread it with a spatula till it's evenly covered. Pour the melted peanut butter over the chocolate in dollops all over the chocolate.
Using a knife or toothpick, swirl the peanut butter over the chocolate to make a marbled effect. Refrigerate this for at least 2 to 3 hours to allow the chocolate to set.
Keep it at room temperature for about 10 to 15 minutes before cutting it. Enjoy this heavenly chocolate and peanut butter bars anytime!