For the bars:
Preheat oven to 325F and line an 8 x 8 inch pan with parchment paper.
In a medium bowl, whisk together almond flour, oat flour, baking powder and salt. In a large bowl, beat butter and erythritol or sugar until creamy. Beat in the eggs and vanilla extract, and then beat in almond flour mixture until dough comes together.
Press dough firmly into prepared pan and smooth top with a flat-bottomed glass. Bake 30 minutes, until just golden brown around the edges and slightly more firm to the touch. Remove and let cool in pan.
For the Icing:
Beat together butter and powdered erythritol or sugar.
Add cream, 1 tablespoon at a time, until desired consistency is achieved. Stir in vanilla and food coloring.
Spread or pipe onto cooled bars.