Illustrator CS5 offers a new feature that can make drawing over letters a lot of fun with a Wacom tablet and any of the natural drawing tools. It’s called the “Draw Inside Mode” and it’s like creating a clipping mask you can doodle in - and instantly clip your scribbles to the shape of your letter.
(If you are working in an earlier version of Adobe Illustrator, I have an alternative method at the end of this post.)
1. Begin with a heavy typeface - I’m using Falstaff MT and I’m starting with the letter a.
2. Next, select the letter and convert it to outlines: Type > Create Outlines. My letter is approximately 2” wide and 1.5” tall. (I also like to keep an extra copy of the original type, before converting, in case I need it later).
You can also choose to keep your font intact, and not convert to outlines - each way offers it's own unique edibility options, so experiment to see what works best for your project.
3. Ungroup once, by choosing Object > Ungroup (your letter should now be identified as a compound path in the top left of the Illustrator control bar). Draw Inside Mode works on single paths, compound paths and type, but not groups. Make an extra copy or 2 in case you need it later.
4. Fill your letter with a color (I’m using a cocoa brown).
5. Select the letter and click on the Drawing Modes icon at the bottom of the Tool Panel and choose the Draw Inside mode. (Dotted lines appear around the letter). Now anything you draw, whether circles, squares or pencil lines, etc. will only show within the shape of the letter.
6. Choose a drawing tool. I’m using the Paintbrush and a calligraphic tip - you can adjust your brush tip and Paintbrush Tool settings to match mine:
Calligraphic Brush Tip Settings (Create New or double-click a tip in the Brushes Panel to change it’s settings)
Angle 45 (Fixed), Roundness 80% (Fixed), Diameter 2 pt, (Pressure), Variation 1 pt., The pressure you use when drawing on your Wacom Tablet will create a subtle variation in line weight with this setting.

Paintbrush Tool Options (Double-click the Paintbrush in the Tool Panel): Fidelity 3, Smoothness 12, Keep Selected. These settings are one of my favorite things about using a Wacom Tablet with Illustrator - this allows you to adjust the drawing tool to add more smoothness (or less) to any marks you make on the Wacom Tablet - good for shaky-hand days - and you can't do this in Photoshop.
7. Deselect the letter, select a color for your linework (I’m using a peachy-pink).
8. Draw over the letter, your brushwork will be clipped to the shape of the letter when you lift your pen.

If you make a line you don’t like, you can delete it right away with the delete key because we chose “Keep Selected” in the Paintbrush Options.
To edit the contents of the mask to delete a brush stroke, Choose Edit> Clipping Mask> Edit Contents (or click the Edit Contents button on the Control Bar.) This will highlight all the doodles inside the letter. With your white arrow you can select and delete a path inside the mask.
Editing within the mask can be a delicate process if you have a lot of paths. I find it less complicated to just delete a path I don't like right after I draw it (Keep Selected is on), or undo a couple of times. It's easy to start over from scratch if you keep copies of the letter off to the side.
9. Return to the Drawing Modes menu (as you did in Step 5) and select the Draw Normal to return to the default mode. You'll no longer see the dotted lines around your letter, and they will behave as a masked group of objects. Now, on to the next letter!
For Adobe Illustrator versions earlier than CS5, you can take steps 1 and 2, select a fill color for the letter and then use the Eraser Tool to doodle over your letter. Double click the Eraser in the Tool Panel to set it’s options.
The Eraser Tool cuts through solid shapes, so create a background shape or copy the original letter outline and place directly behind your “erased” letter to see the color show through instead of the white of the artboard.
Happy letter-making!