Prepare macaroni according to package directions. Set aside.
In large pot, melt butter over medium high heat. Add skim milk and bring to near boiling. Reduce heat to medium and sprinkle in flour. Whisk vigorously over medium heat for 1-2 minutes. Mixture should be thick and boiling. Slowly add cream, while whisking. Add in salt, pepper, mustard and Worcestershire sauce. Reduce heat to low and continue to stir for about 5 minutes.
In food processor, shred Gouda and Cheddar cheese. Add to pot, stir until thoroughly combined.
Add cooked macaroni to cheese mixture. Pour into a 13x9 dish.
In same food processor bowl process 4 slices of bread to a fine crumb. Add melted butter. Sprinkle over macaroni.
Bake uncovered in a 375 degree oven for 25-30 minutes.
Notes
Don't like gouda? Swap it out! I recommend pairing a fairly strong cheese with the cheddar to get the best flavor.